A gorilla playfully trapping tail of short reptile (9)
I believe the answer is:
alligator
'reptile' is the definition.
(alligator is a kind of reptile)
'a gorilla playfully trapping tail of short' is the wordplay.
'playfully' indicates an anagram (I've seen this in other clues).
'trapping' is an insertion indicator.
'of short' suggests taking the first letters (I've seen 'short' mean this).
The first letter of 'tail' is 't'.
'a'+'gorilla'='agorilla'
'agorilla' anagrammed gives 'alligaor'.
'alligaor' going around 't' is 'ALLIGATOR'.
(Other definitions for alligator that I've seen before include "one bites voraciously?" , "Animal of the crocodile family" , "Amphibious reptile" , "beast to be seen in due course?" , "Broad-snouted snapper?" .)