A verb in the Gnomish Lexicon of the 1910s glossed “to tie” (GL/72), probably based on the early root ᴱ√SERE “twine, tie, bind” from the contemporaneous Qenya Lexicon, whose true form was probably ✱ᴱ√ÞERE (QL/83). In Tolkien’s later writings, √THER was “sew”; see that entry for details.
Gnomish
nud-
verb. to incline head, bend face down
ther-
verb. to tie
A verb appearing as G. nud- “incline head, bend face down” in the Gnomish Lexicon of the 1910s (GL/61), probably based on the early root ᴱ√NUHU “bow, bend down; stoop, sink” (QL/68). There is a similar and probably-related verb G. nunta- “agree” appearing two lines below it.
Neo-Sindarin: For purposes of Neo-Sindarin, I would combine and adapt these verbs as ᴺS. nunna- “to incline head, bend face down, ✱nod; to assent, ✱agree” based on the later root √NU “sink, go down”, perhaps from primitive ✱nun-tā.