Lethargic; quiet (6)
I believe the answer is:
sleepy
This clue is a double definition.
'lethargic' is the first definition.
(I've seen this before)
'quiet' is the second definition.
(I've seen this before)
(Other definitions for sleepy that I've seen before include "Drowsy - without excitement" , "Feeling like having a snooze" , "Somnolent" , "(Of place) low in activity" , "Lethargic" .)