Animal of the most agile kind? (4)
I believe the answer is:
stag
'animal' is the definition.
(stag is a kind of animal)
'of the most agile kind?' is the wordplay.
'of' says the answer is hidden in the clue.
'STAG' can be found hidden inside 'most agile kind'.
(Other definitions for stag that I've seen before include "Excluding women" , "Male-only" , "One who speculates" , "Share speculator" , "Investor" .)