Valentine's Day flower (4)
I believe the answer is:
rose
'valentine's day flower' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rose that I've seen before include "'A . . . . by any other name smells as sweet'" , "vacated bed" , "Prickly shrub with bright flowers" , "18 [ROSE]" , "Stood" .)