Calm retort (5)
I believe the answer is:
still
I believe this is a double definition.
'calm' is the first definition.
(I know that calm can be written as still)
'retort?' is the second definition.
(thesaurus)
(Other definitions for still that I've seen before include "'Quiet!'" , "Stop" , "gentle" , "Snap" , "in spite of this" .)