Priceless to begin with — a French play on words (3)
I believe the answer is:
pun
'play on words' is the definition.
('pun' can be a synonym of 'play on words')
'priceless to begin with a french' is the wordplay.
'to begin with' suggests taking the first letters.
'a french' becomes 'un' ('a' in French).
The initial letter of 'priceless' is 'p'.
'p'+'un'='PUN'
(Other definitions for pun that I've seen before include "A play on words, may be funny" , "Double entendre" , "joke" , "Humorous play on words" , "Bit of paronomasia; witticism" .)