The Sindarin equivalent of Q. má, likewise derived from the root √MAH or √MAƷ “hand; handle, wield” (PE17/162; VT47/6). However, in Sindarin this word was archaic, used only in poetry, having been replaced in ordinary speech by other words like S. mâb and (less often) cam. Other remnants of this word can be seen in compounds like molif “wrist, (orig.) hand link” and directional words like forvo and harvo for left and right hand side.
Conceptual Development: In the Gnomish Lexicon of the 1910s, G. mô from the early root ᴱ√MAHA was the normal word for “hand”, replacing mab “hand” (< ᴱ√MAHA) which in this document Tolkien decided was instead an irregular dual form of mô (GL/55). It had also had an irregular plural mabin based on this dual, replacing an older plural †maith. In the Gnomish Grammar, its archaic form was †mâ, with the usual Gnomish sound change of ā to ō (GG/14), as opposed to later Sindarin/Noldorin ā to au, spelt -aw when final. Tolkien seems to have abandoned mô as a non-archaic word for “hand” early on, preferring ᴱN. mab “hand” by the 1920s and introducing N. cam “hand” in the 1930s.
A common Sindarin word for “hand”, most notably an element in the names Camlost “Empty-handed” and Erchamion “One-handed”. In drafts of Tolkien’s 1968 notes on Eldarin Hands, Fingers and Numerals, he glossed this word as “handful, holding hand” (VT47/22 note #19). In the final version of these notes, Tolkien said that its Quenya equivalent camba “referred to the whole hand, but as flexed, with fingers more or less closed, cupped, in the attitude of receiving or holding” (VT47/7), and in the Silmarillion Appendix Christopher Tolkien indicated the same was true of the Sindarin word (SA/cam).
However, based on the 1950s phrase sí il chem en i Naugrim en ir Ellath thor den ammen “✱now all (?hands) of the Dwarves and Elves will be (?against) to us” (VT50/5), I think the Sindarin word is more general in meaning, able to refer to a hand in any context, but most specifically an open hand or one holding an object loosely, as opposed to paur for a tightly closed hand. Based on the gloss “handful”, it seems it could also be used as a unit of measure for the contents of a hand (potential or actual): cam miriain “a hand[ful] of coins”.
Conceptual Development: A possible precursor to this word was G. gob “hollow of hand” from the Gnomish Lexicon of the 1910s based on the early root ᴱ√kop- “keep, guard” (GL/40; QL/47). In The Etymologies of the 1930s the word was N. cam “hand” derived from the root ᴹ√KAB “hollow” (Ety/KAB), a form Tolkien retained thereafter. In later notes he usually derived this word from √KAB (VT47/7, 20), though in one place he considered deriving it from √KAM instead (VT47/20); this root change seems to have been a transient idea.