Favoured expression about island is temporary (7)
I believe the answer is:
interim
'temporary' is the definition.
('interim' can be similar in meaning to 'temporary')
'favoured expression about island' is the wordplay.
'favoured' becomes 'in' (I've seen this in other clues).
'expression' becomes 'term' (I've seen this before).
'about' indicates putting letters inside.
'island' becomes 'i'.
'term' enclosing 'i' is 'terim'.
'in'+'terim'='INTERIM'
'is' is the link.
(Other definitions for interim that I've seen before include "temporary period" , "acting" , "Stopgap" , "Meanwhile" , "Temporary - provisional" .)