Strait-laced girl's flower? (8)
I believe the answer is:
primrose
'flower?' is the definition.
(thesaurus)
'strait-laced girl's' is the wordplay.
'strait-laced' becomes 'prim' ('prim' can be a synonym of 'strait-laced').
'girl' becomes 'rose' (**).
'prim'+'rose'='PRIMROSE'
(Other definitions for primrose that I've seen before include "Pale yellow flower" , "Pale yellow- a primula" , "Woodland plant with pale yellow flowers" , "Early spring flower" , "Spring woodland flower" .)