Be back in frills and checks (7)
I believe the answer is:
rebuffs
'checks' is the definition.
(I've seen this before)
'be back in frills' is the wordplay.
'back' is a reversal indicator.
'in' indicates putting letters inside.
'frills' becomes 'ruffs' (both are decorative flourishes on a garment).
'be' written backwards gives 'eb'.
'eb' placed inside 'ruffs' is 'REBUFFS'.
'and' acts as a link.
(Other definitions for rebuffs that I've seen before include "Snubs" , "Rejects abruptly" , "Rejects outright and bluntly" , "Checks" , "Brushes off" .)