Secure article in trap (4)
I believe the answer is:
gain
'secure' is the definition.
(gaining is a kind of securing)
'article in trap' is the wordplay.
'article' becomes 'a' (indefinite article).
'in' means one lot of letters goes inside another.
'trap' becomes 'gin' (I've seen this before).
'a' inserted inside 'gin' is 'GAIN'.
(Other definitions for gain that I've seen before include "Benefit; put on (weight)" , "reward" , "Obtain, secure" , "Profit; acquire" , "Increase; secure" .)