Warship poised to catch semiaquatic animal (5)
I believe the answer is:
hippo
'semiaquatic animal' is the definition.
(I've seen this before)
'warship poised to catch' is the wordplay.
'to catch' indicates the answer is hidden within the clue (I've seen 'catches' mean this (the answer is caught in the clue)).
'HIPPO' can be found hidden inside 'warship poised'.
(Other definitions for hippo that I've seen before include "Aquatic creature" , "Large African beast (abbr)" , "Mammoth African mammal (abbr)" , "Massive thick-skinned animal of African rivers" , "Augustine looked after" .)