Piano accompanying song or two (4)
I believe the answer is:
pair
'two' is the definition.
(pair is a kind of two)
'piano accompanying song' is the wordplay.
'piano' becomes 'p'.
'accompanying' means one lot of letters go next to another.
'song' becomes 'air' (I've seen this before**).
'p'+'air'='PAIR'
'or' acts as a link.
(Other definitions for pair that I've seen before include "Twins" , "E.g. two aces; mate" , "Husband and wife" , "Duo" , "Put together - two of a kind" .)