A trap is set outside a second time (5)
I believe the answer is:
again
'second time' is the definition.
(I've seen this before)
'a trap is set outside a' is the wordplay.
'a' becomes 'an'.
'trap' is an insertion indicator.
'is set' becomes 'gi' (I can't justify this - if you can you should believe this answer much more).
'outside' is an insertion indicator.
'gi' enclosing 'a' is 'gai'.
'an' enclosing 'gai' is 'AGAIN'.
Can you help me to learn more?
(Other definitions for again that I've seen before include "Here we go ___" , "Next time" , "Ocne more" , "'Another time, once more (5)'" , "One more time, encore" .)