nan- (prefix) "backwards" (NDAN) or "back", as in nanwen- "return" (go/come back, PE17:166), cf. also nanquernë *"turned back", the pl. form of nanquerna _(VT49:17-18). _Apparently assimilated nal- in nalláma "echo" (if this represents nan-láma "back-sound", sound coming back).
Quenya
nalláma
echo
nan-
backwards
nalláma, nallama noun "echo" (LAM). The initial element may be nan- "back", hence "back-sound", sound that comes back (cf. láma).