Copy one found in the writer’s gallery (7)
I believe the answer is:
imitate
'copy' is the definition.
(synonyms)
'one found in the writer's gallery' is the wordplay.
'one found' becomes 'i' (I've seen this in other clues).
'in the' means one lot of letters goes inside another.
'writer's' becomes 'im' ('writer's' could mean 'the crossword setter is').
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'im'+'tate'='imtate'
'i' placed inside 'imtate' is 'IMITATE'.
(Other definitions for imitate that I've seen before include "I ate Tim! (anag.)" , "Reproduce" , "Copy someone" , "Fake" , "I tame it to copy it" .)