Penny and Scotsman love quietly (5)
I believe the answer is:
piano
'quietly' is the definition.
(synonyms)
'penny and scotsman love' is the wordplay.
'penny' becomes 'p'.
'and' says to put letters next to each other.
'scotsman' becomes 'ian' (common Scottish name).
'love' becomes 'o' (love means zero in tennis).
'p'+'ian'+'o'='PIANO'
(Other definitions for piano that I've seen before include "Soft, softly (music)" , "Instrument with ivories" , "In music, soflty" , "Opposite of forte" , "Musical instrument - softly, please" .)