calm down

relax; make relaxed

relaxed, "cooled off"

becoming calm; making calm

Stoppit and Tidyup was a BBC television series released in 1988, created by Charlie Mills and Terry Brain, the duo behind CMTB Animation who had previously created a claymation called The Trap Door. The series was narrated by Terry Wogan. Apart from the main characters Stoppit, a red ball of fluff, and Tidyup, a gherkin-loving purple lump, the supporting characters included Comb Your Hair, Wash Your Face, Hurry Up, Go and Play, Calm Down, Not Now, Bee Have, Bee Quiet, Go to Bed, Don't Do That, Take Care, Eat Your Greens, Clean Your Teeth and the big, bad I Said No, not to mention Say Please And Say Thank You. There are also extra characters called Naughties and Sit Downs, and they all live in the mythical land of Do As You're Told. Each episode was five minutes in length.
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Verb
1. become quiet or calm, especially after a state of agitation; "After the fight both men need to cool off."; "It took a while after the baby was born for things to settle down again."
(synonym) calm, cool off, chill out, simmer down, settle down, cool it
(hypernym) change state, turn
2. make calm or still; "quiet the dragons of worry and fear"
(synonym) calm, quiet, tranquilize, tranquillize, tranquillise, quieten, lull, still
(hypernym) comfort, soothe, console, solace
(hyponym) lull
3. become quiet or less intensive; "the fighting lulled for a moment"
(synonym) lull
(hypernym) hush, quieten, silence, still, shut up, hush up

not be so upset, chill out Please calm down, Mr. Tse. Your daughter is safe.

CALMARE. CALMARSI. PLACARE. PLACARSI. ACQUIETARSI