One barking, not loudly, could be Romeo? (5)
I believe the answer is:
wooer
'could be romeo?' is the definition.
'one barking not loudly' is the wordplay.
'one barking' becomes 'woofer'.
'not' indicates named letters should be taken away.
'loudly' becomes 'f' (A musical term).
'woofer' with 'f' taken away is 'WOOER'.
(Other definitions for wooer that I've seen before include "person to court" , "Man courting a woman" , "Romantic type" , "Suitor" , "One who goes to court" .)