An afternoon rest or sleep (6)
I believe the answer is:
siesta
I believe this is a double definition.
'an afternoon rest' is the first definition.
(I've seen this in another clue)
'sleep' is the second definition.
(I've seen this before)
(Other definitions for siesta that I've seen before include "rest of the Spaniards" , "A mid-day nap in Spain" , "Spanish afternoon nap" , "Afternoon nap in a warm climate" , "Rest in the heat of the day" .)