I have to go after month with European fool (7)
I believe the answer is:
deceive
'fool' is the definition.
(I know that fool is a more specific form of deceive)
'i have to go after month with european' is the wordplay.
'i have' becomes 'I've' (contraction of 'I have').
'to go after' means one lot of letters go next to another.
'month' becomes 'dec' (abbreviation for December).
'with' means one lot of letters go next to another.
'european' becomes 'e' (abbreviation e.g. EU).
'dec'+'e'='dece'
'ive' after 'dece' is 'DECEIVE'.
(Other definitions for deceive that I've seen before include "Intentionally mislead" , "Give a wrong impression to" , "Cheat or mislead" , "Mislead, delude" , "Delude or betray" .)