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?' is a reversal indicator (I've seen 'back' mean this).
'sit' in reverse letter order is 'TIS'.
'can' is the 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" .)