Flirt with many a friend (5)
I believe the answer is:
dally
'flirt' is the definition.
(synonyms)
'with many a friend' is the wordplay.
'with' means one lot of letters go next to another.
'many' becomes 'D' (Roman numeral for 500).
'a friend' becomes 'ally' (an ally is a friend or supporter).
'd' put next to 'ally' is 'DALLY'.
(Other definitions for dally that I've seen before include "Waste time" , "Move slowly" , "Procrastinate" , "Trifle" , "Dawdle - delay" .)