Addict initially kicks it in a month.. (6)
I believe the answer is:
junkie
'addict' is the definition.
(I know that addict can be written as junkie)
'initially kicks it in a month' is the wordplay.
'initially' suggests taking the first letters.
'in' is an insertion indicator.
'a month' becomes 'june' (June is an example).
The first letters of 'kicks it' is 'ki'.
'ki' put within 'june' is 'JUNKIE'.
(Other definitions for junkie that I've seen before include "In slang, a drug addict" , "User" , "one shooting up" , "Jargon for a drug addict" .)