Flower in formal lines, we hear (8)
I believe the answer is:
primrose
'flower' is the definition.
(thesaurus)
'formal lines we hear' is the wordplay.
'formal' becomes 'prim' (I've seen this in other clues).
'lines' becomes 'rows' (row is a kind of line).
'we hear' shows a homophone (sound like).
'rows' sounds like 'rose'.
'prim'+'rose'='PRIMROSE'
'in' is the link.
(Other definitions for primrose that I've seen before include "Pale yellow flower" , "Woodland plant with yellow flowers in spring" , "something in the bed!" , "Rip morse up to find the flower" , "grows wild" .)