An afternoon rest (6)
I believe the answer is:
siesta
'an afternoon rest' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for siesta that I've seen before include "Forty winks" , "Seat is found for a Spanish rest period" , "Catnap" , "Afternoon nap in a warm climate" , "After lunch nap" .)