Following proper sex this compiler's crude (9)
I believe the answer is:
primitive
'crude' is the definition.
(synonyms)
'following proper sex this compiler's' is the wordplay.
'following' is a charade indicator (letters next to each other).
'proper' becomes 'prim' (prim and proper).
'sex' becomes 'it' (common euphemism).
'this compiler's' becomes 'i've' ('I have' referring to the crossword setter).
'prim' next to 'it' is 'primit'.
'primit'+'ive'='PRIMITIVE'
(Other definitions for primitive that I've seen before include "Unsophisticated - crude" , "Early - simple - crude" , "Ancient" , "At a very early stage of development" , "Characteristic of early uncivilised period" .)