Another name for the Noldor appearing in name lists and The Etymologies from the 1930s (LR/403, Ety/IS). It seems to be a combination of istima “wise” and the plural of the agental suffix -mo. It was initially written as Ainimor.
Quenya
Istimor
wise ones
Istimor pl. noun *"Wise Ones" = "Gnomes" (Noldor) (IS). Sg. #Istimo.