Mistake crossing Irish animal (7)
I believe the answer is:
giraffe
'animal' is the definition.
(thesaurus)
'mistake crossing irish' is the wordplay.
'mistake' becomes 'gaffe' (gaffe is a kind of mistake**).
'crossing' indicates putting letters inside.
'irish' becomes 'ir' (abbreviation).
'gaffe' going around 'ir' is 'GIRAFFE'.
(Other definitions for giraffe that I've seen before include "Animal once known as a camelopard" , "The tallest animal with long neck" , "Tallest beast" , "wild beast" , "Long-necked animal" .)