Holiday island, manic or otherwise (7)
I believe the answer is:
minorca
'holiday island' is the definition.
(I've seen this before)
'manic or otherwise' is the wordplay.
'otherwise' indicates anagramming the letters.
'manic'+'or'='manicor'
'manicor' with letters rearranged gives 'MINORCA'.
(Other definitions for minorca that I've seen before include "Balearic island (Eng. sp.)" , "Land in Balearics" , "Mediterranean island" , "holiday island" , "One of Balearic islands" .)