Forbidden love in abandoned boat (5)
I believe the answer is:
'forbidden' is the definition.
'love in abandoned boat' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'in' is an insertion indicator.
'abandoned' indicates an anagram.
'boat' is an anagram of 'tabo'.
'o' placed into 'tabo' is 'TABOO'.
(Other definitions for taboo that I've seen before include "Forbidden for social reasons", "Not to be touched or used, banned for religious reasons", "Not permitted", "(Irrational) prohibition", "unacceptable".)