Garments clothing ancients, primarily ... (5)
I believe the answer is:
togas
'garments clothing ancients primarily' is the definition.
I can't judge whether this definition defines the answer.
'garments clothing ancients' is the wordplay.
'garments' becomes 'togs' ('tog' can be a synonym of 'garment').
'clothing' means one lot of letters goes inside another (some letters cover up or clothe others).
'ancients' becomes 'a' (this could be a standard abbreviation I've not previously seen).
'togs' enclosing 'a' is 'TOGAS'.
Can you help me to learn more?
(Other definitions for togas that I've seen before include "What some ancient citizens wore" , "Roman garments" , "garments worn by ancient Romans" , "clothing" .)