Yes, yes, yes! (4)
I believe the answer is:
okay
'yes' is the definition.
(thesaurus)
'yes yes' is the wordplay.
'yes' becomes 'ok' (both are affirmative answers).
'yes' becomes 'ay' ().
'ok'+'ay'='OKAY'
(Other definitions for okay that I've seen before include "Fairly good; approve" , "Correct" , "Not terrific but acceptable" , "in order" , "Permissible (colloq.)" .)