This bread is mine, thank you (5)
I believe the answer is:
pitta
'this bread' is the definition.
(pitta is a type of bread)
'mine thank you' is the wordplay.
'mine' becomes 'pit' (as in a mining pit).
'thank you' becomes 'ta' (informal way of saying thank you).
'pit'+'ta'='PITTA'
'is' acts as a link.
(Other definitions for pitta that I've seen before include "Flat hollow unleavened bread" , "Partially-leavened bread of the Near East" , "Greek unleavened bread" , "Flat sort of bread" , "Slightly leavened bread" .)