Rodent found in crate (3)
I believe the answer is:
rat
'rodent' is the definition.
(rat is a kind of rodent)
'in crate' is the wordplay.
'in' says the answer is hidden in the clue.
'RAT' is hidden in the letters of 'crate'.
'found' is the link.
(Other definitions for rat that I've seen before include "Treacherous person" , "Rodent - deserter" , "Betray like a rodent" , "Renegade" , "one who deserts the sinking ship?" .)