A noun for “claw, talon” appearing in rough notes on Elvish Hands, Fingers and Numerals from the late 1960s based on the root √NAP “grasp, seize quickly” (VT47/20). In the margin Tolkien wrote a variant form namma with the same glosses, perhaps from ✱nap-mā and reflecting the earlier (pre-1960) development whereby *pm* > *bm* > *mm* (hat-tip to Vyacheslav Stepanov for this suggestion). If so, nappa may also be derived from ✱nap-mā, with the (post-1960) development whereby *pm* > *pƕ* > *pp*.
Neo-Quenya: For purposes of Neo-Quenya, I’d stick to nappa, and avoid the question of its origin by assuming it is from ✱nappā.
nappa noun "claw, talon" (also namma) (VT47:20)