Devil of a strange omen to many! (5)
I believe the answer is:
demon
'devil' is the definition.
('demon' can be a synonym of 'devil')
'a strange omen to many' is the wordplay.
'a strange' indicates an anagram.
'to' means one lot of letters go next to another (I've seen this in other clues).
'many' becomes 'd' (**).
'omen' anagrammed gives 'emon'.
'emon' after 'd' is 'DEMON'.
'of' is the link.
(Other definitions for demon that I've seen before include "Fanatic; devil" , "Imp" , "Inspiring force" , "Skilful person" , "Expert" .)