كثرIbn Fāris's own chapter entry for ك‑ث‑ر is not among the excerpts given; per al-Khalīl … (root kthr)

[al-kathra (الكثرة): the increase/growth of number]. kathura (كَثُرَ) the thing kathratan (كَثْرَةً), so it is kathīr (كَثِيرٌ) [numerous]. And [you say]: kāthar-nāhum [fa-kathar-nāhum] (كَاثَرْنَاهُمْ فَكَثَرْنَاهُمْ) [we vied with them in numbers and outnumbered them]. And kaththara (كَثَّرَ) the thing: he made it many (akthara-hu), and qallala it: he made it few. A man mukthir (مُكْثِرٌ): one with much wealth. A man makthūr ʿalayhi (مَكْثُورٌ عَلَيْهِ), i.e., many are those seeking his generosity/favor. A man miktār (مِكْثَارٌ) and a woman miktār (مِكْثَارٌ): the two who talk much. akthartu (أَكْثَرْتُ) the thing and kaththartu-hu (كَثَّرْتُهُ): I made it many/abundant. Al-Kawthar (الكَوْثَرُ): a river in Paradise from which most of the rivers of Paradise branch off. From ʿĀʾisha: 'Whoever wants to hear the murmur of al-Kawthar, let him put his finger in his ear.' And it is said: rather al-Kawthar is the abundant good that the Prophet (ﷺ) was given. Al-kathr (الكَثْرُ) [and al-kuthr]: the pith/heart of the palm tree (jummār an-nakhl), and it is said: al-kathr is al-jadhb (الجَذْب), which is also the palm-heart. Al-Ḍarīr said: al-jadhb is a palm that grows within the trunks of [other] palm trees, so it is pulled out (yujdhab), and its pith is eaten, i.e., it is extracted.

Al-kathra (الكَثْرَةُ) is the opposite of scarcity (al-qilla). Do not say al-kithra with kasra, for that is a poor/incorrect dialect form. One says kathura (كَثُرَ) the thing, so it is kathīr (كَثِيرٌ). A people (qawm) kathīr, and they are kathīrūn. akthara (أَكْثَرَ) the man, i.e., his wealth became abundant. And it is said: kāthar-nāhum fa-kathar-nāhum (كَاثَرْنَاهُمْ فَكَثَرْنَاهُمْ), i.e., we overcame/outdid them in numbers. From this is the saying of al-Kumayt describing dogs and a bull: "And it ravaged in the soft ground therein with delving," "the slaughter of the matched-one and the outnumbered-one, opportuning." Al-ʿathʿatha (العَثْعَثَةُ) is soft ground. Al-mukāfiʾ (المُكَافِئُ) is one who slaughters two sheep, one matching the other, for the ʿaqīqa [birth sacrifice]. Yahtabil (يَهْتَبِلُ): he seizes an opportunity and schemes. istakthartu (اسْتَكْثَرْتُ) from the thing, i.e., I sought/took much of it. Al-kuthr (الكُثْرُ) with ḍamma, referring to wealth: the abundant [amount]. And it is said: 'He has neither little (qill) nor much (kuthr).' Abū ʿAmr cited for a man of Rabīʿa: "For indeed al-kuthr (abundance) has wearied me long ago," "and I was not stingy/frugal since I was a boy." One says: 'Praise be to God for the little and the much' (al-qill wa-l-kuthr), and (al-qull wa-l-kuthr). At-takāthur (التَّكَاثُرُ) is al-mukāthara (mutual outdoing in numbers). ʿadad kāthir (عَدَدٌ كَاثِرٌ), i.e., numerous. Al-Aʿshā said: "And I am not more abundant than them in pebbles [i.e., number]," "but indeed glory belongs to the one who outnumbers (al-kāthir)." And so-and-so 'boasts of abundance' (yatakaththaru) with someone else's wealth. Ibn al-Sikkīt: so-and-so is makthūr ʿalayhi (مَكْثُورٌ عَلَيْهِ) when what he had is exhausted and claims/obligations upon him have multiplied, like mathmūd, mashfūh, and maḍfūf. Al-Kawthar among men: the master abundant in good. Al-Kumayt said: "And you, O son of Marwān, are abundant (kathīr) and good," "and your father, son of the nobles, was a Kawthar." Al-Kawthar of dust: the abundant [cloud of dust]. And it has become 'tukawthira' (تَكَوْثَرَ) [grown abundant]. The poet said: "And the dust of death rose until it became abundant (takawthara)." And al-Kawthar: a river in Paradise. Al-kuthār (الكُثَارُ) with ḍamma: the abundant. Al-kathr (الكَثْرُ): the pith of the palm tree (jummār an-nakhl), and it is said [to mean] its spadix/inflorescence (ṭalʿ). In the ḥadīth: 'There is no [hand-]cutting [punishment] for [theft of] fruit or for al-kathr.' And the palm tree has produced its spadix (akthara), i.e., put forth its ṭalʿ.

It has already been mentioned that abundance (al-kathra) and scarcity (al-qilla) are used regarding discrete quantity, such as numbers. He (God) said, Most High: 'And it will surely increase many of them (wa-la-yazīdanna kathīran)' [al-Māʾida/64]; 'and most of them (aktharuhum) dislike the truth' [al-Muʾminūn/70]; 'rather most of them (aktharuhum) do not know the truth' [al-Anbiyāʾ/24]. He said: 'How many a small company (fiʾa qalīla) has overcome a large company (fiʾa kathīra)' [al-Baqara/249]. And He said: 'and scattered from both of them many men (rijālan kathīran) and women' [al-Nisāʾ/1]; 'many (kathīr) of the People of the Book wished' [al-Baqara/109] — up to many verses [using this term]. And His saying 'with abundant fruit (fākiha kathīra)' [Ṣād/51]: He made it abundant in comparison with the foods of this world; and abundance here does not refer to number alone but also to excellence/superiority. One says: number kathīr, kuthār, kāthir — meaning surplus/exceeding. And a man kāthir: when he is abundant in wealth. The poet said:

Al-kathra, al-kithra, and al-kuthr: the opposite of scarcity (al-qilla). Al-Tahdhīb: Do not say al-kithra with kasra, for it is a poor/incorrect dialect form. A people (qawm) kathīr, and they are kathīrūn. Al-Layth: al-kathra is the increase of number. One says: kathura the thing, yakthuru, kathratan, so it is kathīr. And kaththara the thing: he made it many; and qallala it: he made it few. Al-kuthr with ḍamma, regarding wealth: the abundant. One says: 'He has neither little (qill) nor much (kuthr).' Abū ʿAmr cited for a man of Rabīʿa: "For indeed al-kuthr has wearied me long ago," "and I was not stingy since I was a boy." Ibn Barrī said: the poem is by ʿAmr ibn Ḥassān of Banū al-Ḥārith ibn Hammām. He says: seeking abundance of wealth has wearied me, though I have not been stingy from my youth to my old age — so I am neither among those with much nor those who are stingy. He said: he says this to his wife; she had reproached him regarding two she-camels (nāb) which he had slaughtered for a guest who had come to him named Isāf, and he said: 'Is it concerning two she-camels that Isāf received / that my divorced wife laments, unable to sleep?' 'Do you consider — have you seen Abū Qubays [i.e., al-Nuʿmān ibn al-Mundhir, diminutively named] / whose life the abundant, accumulated blessings (al-niʿam al-rukām) prolonged?' 'He built at al-Ghamr a lofty, towering [edifice] / in whose galleries the doves cooed.' 'Death-throes seized him on an appointed day / — and every pregnant female has her term.' 'And Chosroes — when his sons divided him / with swords, as flesh is divided.' He means by Abū Qubays al-Nuʿmān ibn al-Mundhir, whose kunya was Abū Qābūs, so he diminutized it as a diminutive of curtailment (tarkhīm). Al-rukām: the abundant; he means: if abundance of wealth could grant anyone immortality, it would have granted immortality to Abū Qābūs. Al-ṭawāʾiq: the structures built with fired brick. A thing kathīr and kuthār: like ṭawīl and ṭuwāl [long forms]. One says: 'Praise be to God for the little and the much' (al-qill wa-l-kuthr, and al-qull wa-l-kuthr). In the ḥadīth: 'Excellent wealth is forty, and al-kuthr [the abundant threshold] is sixty' — al-kuthr with ḍamma means 'the abundant,' like al-qill for 'the little'; and al-kuthr is the bulk/greater part of a thing and its maximum. kathura the thing, kathāratan, so it is kathīr, kuthār, and kathr. And His saying, Most High: 'and curse them with a curse kathīran (abundant)' — Thaʿlab said: its meaning is 'persist upon him [with the curse]'; and this relates back to the same idea, because if one persists upon something, it becomes abundant/frequent. kaththara the thing: he made it many/abundant. akthara: he brought much; and it is said: kaththara the thing and akthara-hu [both mean] he made it many. akthara-Llāhu fīnā mithlaka: 'may God increase among us [the like of] you' — meaning 'bring in'; Sībawayh related this. akthara the man: his wealth became abundant. In the ḥadīth of al-ifk (the slander): '...and she had co-wives, none of whom but kaththarna [multiplied talk] concerning her,' meaning they multiplied speech about her and were harsh toward her; and in it also: 'Ḥassān was among those who kathara ʿalayhā [spoke excessively against her]' — also transmitted with the letter bāʾ [kabbara?], as mentioned previously. A man mukthir: possessor of kuthr [abundant wealth]; miktār and miktīr: much-talking, and likewise the feminine without the tāʾ marbūṭa. Sībawayh said: it is not pluralized with wāw and nūn, because its feminine form does not take the tāʾ marbūṭa. Al-kāthir: the abundant. ʿadad kāthir: numerous. Al-Aʿshā said: [entry continues]