دأمSuccession and superimposition — one thing piled or pressed upon another, per Ibn Fāris. (root dm)

The lexicographers in chronological order, from al-Khalīl to Lane.

Al-Khalīl gives the base sense as propping a wall by shoving it down bodily onto something in a low place (in a single motion): daʾamtahu ʿalayhi; and he already has the extended tadaʾʾum of waves, terrors and cares 'piling upon' a man, citing the verse taḥta ẓilāli l-mawji idh tadaʾʾamā. Al-Jawharī keeps both strands: tadaʾʾama l-māʾu l-shayʾ, 'the water engulfed it'; tadaʾʾama l-faḥl al-nāqa, 'the stallion mounted/covered the she-camel'; tadāʾamahu l-amr, 'the affair piled up and pressed upon him'; and al-daʾmāʾ, 'the sea,' on the pattern faʿlāʾ; daʾamtu l-ḥāʾiṭ, 'I propped up the wall,' a synonym of daʿamtu. Ibn Fāris (Maqāyīs) crystallizes the root as tawālin wa-tanaḍud, 'succession and stacking' — one thing atop another — and treats the wall-propping sense as an instance of this, since propping puts one thing over/against another. Ibn Manẓūr (Lisān) reproduces and organizes these: daʾm as a single forceful push of a wall onto something in a depression; tadāʾamat/tadaʾʾamathu for things (terrors, cares, waves, rain) accumulating and crashing one atop another; daʾm also glossed simply as 'whatever covers you.' No entry survives for this root in al-Rāghib's Mufradāt (unsurprising, since it is absent from the Qurʾān) or in the Lane excerpt given.

What the theorists of sound symbolism would say of these letters. Speculative by nature.

أ carries no entry in the correspondences given, so only د and م can be weighed. Al-Dabbāgh reads د (fatḥa) as an indication of something external to the self, and م as 'all created beings'; al-Akbarī's cosmological table assigns د to the lowest heaven and م to the human being. Read together and loosely, these might be taken to echo the root's sense of an external mass — waves, terrors, a mounting stallion — bearing down upon or piling onto a self/created being, which is suggestively consonant with dāʾim/tadaʾʾum's imagery of engulfment. This remains explicitly speculative letter-symbolism, not linguistic evidence in the ordinary sense.

The two-letter nucleus (Ibn Fāris's own chapters) and the permutations of the letters (Ibn Jinnī).

Ibn Fāris's own neighboring d-ʾ chapters give: daʾaba (steady persistence, custom), daʾala (a light, nimble gait), daʾaẓa (fullness, packing something into a container), and daʾiya (deception; also a bone-joint, something connected to and resembling another) — dāʾith he explicitly rejects as a true chapter, being a metathesis of thaʾdāʾ. Set beside these, dāʾama's own sense of 'succession/stacking' sits comfortably among siblings that all touch, loosely, on persistence, connection, or packed accumulation. Among the permutations, أدم (concord, reconciling two parties — yuʾdamu baynahumā) and أمد (al-amad, 'the utmost point/limit,' occurring 4 times in the Qurʾān) are also independently attested and glossed, while دمأ, مدأ are unattested and مأد attested but ungloss­ed here. One could juxtapose دأم (piling-together), أدم (bringing-together in concord), and أمد (a point one is brought toward/up to) as a family gesturing at 'joining, converging, or bearing down to a point' — but this is Ibn Jinnī–style greater-derivation speculation, not something Ibn Fāris himself asserts for this cluster.

Cognates in the sister languages, and whether the word was borrowed.

No confident Semitic cognate for دأم in this specific sense (propping/piling/engulfing) is known to me. The root is thinly attested even within Arabic (absent from the Qurʾān, a modest lexicographic entry), and I have no reliable comparative data from Hebrew, Aramaic, Akkadian, or Geʿez to cite here. It should be treated as a native but lexically minor Arabic root rather than assigned a cognate or loan origin.