Second person to sound like a sheep (3)
I believe the answer is:
you
'second person' is the definition.
(second person pronoun)
'sound like a sheep' is the wordplay.
'sound like' shows a homophone (sound like).
'a sheep' becomes 'ewe' (a ewe is a female sheep).
'ewe' is a homophone of 'YOU'.
'to' is the link.
(Other definitions for you that I've seen before include "Person speaker addresses" , "Thou" , "Neither me, nor him" , "Second person pronoun" , "Person being addressed" .)