One's caught in a trap once more (5)
I believe the answer is:
again
'once more' is the definition.
(synonyms)
'one's caught in a trap' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'caught in' is an insertion indicator.
'trap' becomes 'gin' (gin trap is a kind of animal trap).
'a'+'gin'='agin'
'a' going within 'agin' is 'AGAIN'.
(Other definitions for again that I've seen before include "Ocne more" , "repeat order" , "Not for the first time" , "second term" , "Repeatedly" .)