One piece of music or twenty (5)
I believe the answer is:
score
I believe this is a triple definition!
'one piece' is the first definition.
(score is a kind of piece)
'of' acts as a link.
'music' is the second definition.
(score is a kind of music)
'or' acts as a link.
'twenty' is the third definition.
(synonyms)
(Other definitions for score that I've seen before include "Chalk up - twenty" , "Twenty; scratch" , "Musical composition in written form" , "Mark; twenty" , "Points in a match" .)