Strange one with a rum charm (7)
I believe the answer is:
enamour
'charm' is the definition.
(synonyms)
'strange one with a rum' is the wordplay.
'strange' is an anagram indicator.
'with' says to put letters next to each other.
'a'+'rum'='arum'
'one' put after 'arum' is 'arumone'.
'arumone' anagrammed gives 'ENAMOUR'.
(Other definitions for enamour that I've seen before include "Fill with love" , "entrance" , "Our name (anag)" , "sweep one off one's feet" , "Charm, captivate" .)