Calm yet just quits (4)
I believe the answer is:
even
This clue is a quadruple definition!!
'calm' is the first definition.
(I've seen this before)
'yet' is the second definition.
(synonyms)
'just' is the third definition.
(thesaurus)
'quits' is the fourth definition.
(as in 'call it quits')
(Other definitions for even that I've seen before include "night" , "exact" , "Yet; level" , "Steady or smooth" , "Yet; smooth" .)