Calm, showing little emotion (6)
I believe the answer is:
stolid
I believe this is a double definition.
'calm' is the first definition.
(thesaurus)
'showing little emotion' is the second definition.
(I've seen this before)
(Other definitions for stolid that I've seen before include "Not excitable, unemotional" , "cool" , "Impassive or apathetic" , "Bovine" , "Calm, unanimated" .)