Verbs

(v)sedate, calm, tranquilize, tranquillize, tranquillisecause to be calm or quiet as by administering a sedative to“The patient must be sedated before the operation”

Adjectives

(s)sedate, staidcharacterized by dignity and propriety
(s)grave, sedate, sober, solemndignified and somber in manner or character and committed to keeping promises“a grave God-fearing man”, “a quiet sedate nature”, “as sober as a judge”, “a solemn promise”, “the judge was solemn as he pronounced sentence”