Copy: one friend keeps it (7)
I believe the answer is:
imitate
'copy' is the definition.
(I know that copy can be written as imitate)
'one friend keeps it' is the wordplay.
'one' becomes 'I' (Roman numeral).
'friend' becomes 'mate' (mate is a kind of friend).
'keeps' indicates putting letters inside.
'mate' placed around 'it' is 'mitate'.
'i'+'mitate'='IMITATE'
(Other definitions for imitate that I've seen before include "Fake" , "Appear like, in behaviour or appearance" , "Copy, simulate" , "Copy or mimic" , "Follow suit" .)