A few occupying Irish compound (6)
I believe the answer is:
isomer
'compound' is the definition.
(isomer is a kind of compound)
'a few occupying irish' is the wordplay.
'a few' becomes 'some' (I've seen this before).
'occupying' is an insertion indicator.
'irish' becomes 'ir' (abbreviation).
'some' inserted within 'ir' is 'ISOMER'.
(Other definitions for isomer that I've seen before include "Chemical compound - I'm Eros (anag)" , "Compound with same formula but not structure" , "One of two compounds differing in arrangement of the same atoms" , "Atomic nucleus; is more (anag.)" , "Compound sharing a formula with another" .)