Retain or rebuild front (8)
I believe the answer is:
anterior
'front' is the definition.
(similar in meaning)
'retain or rebuild' is the wordplay.
'rebuild' indicates anagramming the letters (I've seen 'rebuilt' mean this).
'retain'+'or'='retainor'
'retainor' is an anagram of 'ANTERIOR'.
(Other definitions for anterior that I've seen before include "Nearer the front; earlier" , "Towards the front" , "Nearer the front or the head" , "Previous, to the fore" , "Located before, in time or place" .)