Saint opposing a time of fasting in East (9)
I believe the answer is:
valentine
'saint' is the definition.
(St Valentine)
'opposing a time of fasting in east' is the wordplay.
'opposing' becomes 'v' (abbreviation for versus).
'time of fasting' becomes 'Lent' (fast leading up to Easter).
'east' becomes 'E' (synonyms).
'v'+'a'+'lent'+'in'+'e'='VALENTINE'
(Other definitions for valentine that I've seen before include "Potential lover" , "Card to sweetheart" , "A loving greeting card sent on February 14th" , "One of Shak.'s Two Gentlemen" , "Message for February 14" .)