Forbidden love in abandoned boat (5)
I believe the answer is:
taboo
'forbidden' is the definition.
(synonyms)
'love in abandoned boat' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'in' indicates putting letters inside.
'abandoned' is an anagram indicator (the original order is abandoned).
'boat' is an anagram of 'tabo'.
'o' inserted into 'tabo' is 'TABOO'.
(Other definitions for taboo that I've seen before include "Ritual prohibition" , "No-no" , "ruled out" , "Not permitted" , "Social prohibition" .)