Especially large spandex undergarment for gorilla bottoms (5)
I believe the answer is:
extra
'especially' is the definition.
(synonyms)
'large spandex undergarment for gorilla bottoms' is the wordplay.
'bottoms' indicates one should take the final letters (I've seen 'bottom of' mean this).
The last letters of 'large spandex undergarment for gorilla' are 'EXTRA'.
(Other definitions for extra that I've seen before include "There's more" , "non-standard item" , "more than is necessary" , "no ball perhaps" , "Ancillary" .)