A semi-romantic smell! (5)
I believe the answer is:
aroma
'smell' is the definition.
(aroma is a kind of smell)
'a semi-romantic' is the wordplay.
'semi-romantic' becomes 'roma' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'roma'='AROMA'
Can you help me to learn more?
(Other definitions for aroma that I've seen before include "Food fragrance" , "Spicy fragrance" , "Distinctive smell" , "Scent - fragrance" , "Redolence" .)