A rum needs to capture island flavour (7)
I believe the answer is:
aniseed
'flavour' is the definition.
(I've seen this before)
'a rum needs to capture island' is the wordplay.
'rum' indicates an anagram (rum can mean strange or unusual).
'to capture' means one lot of letters goes inside another.
'island' becomes 'i'.
'needs' with letters rearranged gives 'nseed'.
'nseed' placed around 'i' is 'niseed'.
'a'+'niseed'='ANISEED'
(Other definitions for aniseed that I've seen before include "Flavouring herb" , "Liquorice flavouring -- ie Danes (anag)" , "Plant" , "Natural flavouring" , "Strong herbal flavouring" .)