It’s in one friend’s copy (7)
I believe the answer is:
imitate
'copy' is the definition.
(synonyms)
'it's in one friend's' is the wordplay.
'it's' becomes 'it' (I've seen this in other clues).
'in' is an insertion indicator.
'one' becomes 'I' (Roman numeral).
'friend' becomes 'mate' (mate is a kind of friend).
'i'+'mate'='imate'
'it' inserted inside 'imate' is 'IMITATE'.
(Other definitions for imitate that I've seen before include "'Ape, copy (7)'" , "Take as a model" , "Mimic or follow as a model" , "I tame it to copy it" , "Copy (mannerisms)" .)