Don't panic
'don't panic' is the definition.
(I've seen this in another clue)
This is all the clue.
'don't panic' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for becalm that I've seen before include "don't get the wind up" , "Make quiet or still - sounds like an order" , "Make still (from lack of wind)" , "Render motionless from lack of wind" , "Make quiet or still - that's an order?" .)