nimetus(1) name, designation, appellation
(2) namelessness
So it's one of those strange words for which the two definitions are more or less opposites of each other.
It can also be the inessive case form of
nimetu "nameless".
Etymology for (1):
nimetama - to name, to designate (stem: nimeta-)
-us - forms nouns from verb stems
Etymology for (2):
nimi - name
-tu - indicates lack of something; -less
-s - forms a noun from a -tu suffix ("state of being without x")