Writer reviewed clip about space (6)
I believe the answer is:
pencil
'writer' is the definition.
(something which writes)
'reviewed clip about space' is the wordplay.
'reviewed' is an anagram indicator (letters reviewed or revised).
'about' is an insertion indicator.
'space' becomes 'en' (in printing, a space as wide as a letter 'n').
'clip' with letters rearranged gives 'pcil'.
'pcil' placed around 'en' is 'PENCIL'.
(Other definitions for pencil that I've seen before include "implement in case?" , "Wooden writer" , "HB writer?" , "American bureaucrat -- purple niches (anag)" , "Writing implement with graphite centre" .)