Confirmation that you can sit back? (3)
I believe the answer is:
tis
'confirmation that you' is the definition.
Although both the answer and 'confirmation' are nouns, they are not in the same form of the noun.
'sit back?' is the wordplay.
'back?' shows that the letters should be reversed in order (I've seen 'backed' mean this).
'sit' backwards is 'TIS'.
'can' acts as a link.
Can you help me to learn more?
(Other definitions for tis that I've seen before include "... the season to be jolly" , "That thing's" , "I confirm the identity of" , "For poet, that's" , "McCourt work" .)