Finally catch or trap insect (6)
I believe the answer is:
hornet
'insect' is the definition.
(hornet is a kind of insect)
'finally catch or trap' is the wordplay.
'finally' says to take the final letters.
'trap' becomes 'net' (net is a kind of trap).
The last letter of 'catch' is 'h'.
'h'+'or'+'net'='HORNET'
(Other definitions for hornet that I've seen before include "Stinging insect" , "Large wasp with vicious sting" , "Throne (anag.)" , "A large wasp with severe sting (6)" , "Small flier" .)