Write in copy, filling empty space (8)
I believe the answer is:
inscribe
'write' is the definition.
(inscribing is a kind of writing)
'in copy filling empty space' is the wordplay.
'copy' becomes 'crib' (crib can mean to copy from another source).
'filling' indicates putting letters inside.
'empty' means to remove the middle letters.
'space' with its middle removed is 'se'.
'crib' put within 'se' is 'scribe'.
'in'+'scribe'='INSCRIBE'
(Other definitions for inscribe that I've seen before include "Engrave or write upon" , "Draw (a figure) within another" , "Write, engrave, or print as a lasting record" , "Engrave; enter (name in list)" , "Write; etch" .)