adjective

not showing or feeling nervousness, anger, or other strong emotions.

she had to keep calm at all costs

noun

the absence of strong emotions; calm feelings.

his usual calm deserted him

composure,coolness,calmness,self-possession,sangfroid,presence of mind,poise,aplomb,self-control,serenity,tranquillity,equanimity,imperturbability,equability,placidness,placidity,impassiveness,impassivity,dispassion,phlegm,stolidity,cool,unflappability,ataraxy,ataraxia

verb

make (someone) tranquil and quiet; soothe.

I took him inside and tried to calm him down

soothe,pacify,placate,mollify,appease,conciliate,hush,lull,gentle,tranquillize,quell,allay,alleviate,assuage,quieten (down),square off,dulcify