A verb in The Etymologies of the 1930s glossed “clothe” and derived from the root ᴹ√KHAP “enfold” (Ety/KHAP), along with a variant N. hamma- of the same meaning (EtyAC/KHAP). In The Etymologies as published in The Lost Road, Christopher Tolkien gave the form of the second verb as hamnia- (LR/363), but Carl Hostetter and Patrick Wynne confirmed that the actual form was hamma- in their Addenda and Corrigenda to the Etymologies (VT45/21).
Conceptual Development: There was a verb of similar meaning in the Gnomish Lexicon of the 1910s: G. {baitha- >>} baidha- “to clothe” (GL/21). This was derived from the early root ᴱ√VAẎA “enfold, wind about” as suggested by Christopher Tolkien (LT1A/Vai; QL/100).
Neo-Sindarin: In The Etymologies, Tolkien made no distinction between N. hab- and N. hamma-, except that the latter seems to be the basis for (the gerund?) N. hammad “clothing”. For purposes of Neo-Sindarin, I would use hab- for any covering of cloth, but would use hamma- for the more specific act of putting on clothing or getting dressed.
The form hamnia- in the Etymologies is a misreading according to VT/45:21