"Cool it!"
'cool it' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for relax that I've seen before include "Unbend" , "Make (rule) less strict" , "Hang loose" , "Moderate" , "Loosen up, slow down" .)
'cool it' is the definition.
(synonyms)
This is all the clue.
(Other definitions for calm down that I've seen before include "Become less agitated" , "still" , "Don't get so upset!" , "Cool it - don't be a mad clown" , "Become more tranquil" .)
(Other definitions for smithsonian that I've seen before include "Washington museum institution" , "Washington research institution" .)