Tactless remark describing Kirk essentially as an animal (7)
I believe the answer is:
giraffe
'an animal' is the definition.
(thesaurus)
'tactless remark describing kirk essentially' is the wordplay.
'tactless remark' becomes 'gaffe' (I've seen this before).
'describing' means one lot of letters goes inside another (describe can mean to form the outline of).
'essentially' says to take the centre.
The centre of 'kirk' is 'ir'.
'gaffe' enclosing 'ir' is 'GIRAFFE'.
'as' is the link.
(Other definitions for giraffe that I've seen before include "Tall creature" , "Lofty browser's" , "The largest ruminant" , "Tallest mammal" , "Tallest beast" .)