Target excellent month (3)
I believe the answer is:
aim
'target' is the definition.
('aim' can be a synonym of 'target')
'excellent month' is the wordplay.
'excellent' becomes 'ai'.
'month' becomes 'm' (standard abbreviation).
'ai'+'m'='AIM'
(Other definitions for aim that I've seen before include "Purpose in directing the rifle" , "Plan" , "mission" , "Point or direct, a weapon say" , "Point (gun); intention" .)