From Proto-Indo-Iranian*namas-(“to bow, prostrate”).
The primary meaning of "bow, salutation" is Rigvedic.
It is an s-stem formed on the basis of the verbal root नम्(nam) (नमति(namati)), meaning "to bend, bow, to submit one's self".
All alternative meanings are limited to glossaries and lexicographies (Naighaṇṭuka and other collections).