Subjects, usually (5)
I believe the answer is:
nouns
'subjects usually' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nouns that I've seen before include "Words referring to person, place or thing" , "They refer to people, places and things" , "Words that can be the subject or object of a verb" , "Words used as names of places or things" , "terms" .)