tranquilizar
/tɾankiliˈθaɾ/ · B1 · verb
to calm, to calm down, to tranquilize
💊😌 tranquil + -izar = make tranquil, so to calm down
It comes from Latin tranquillus, meaning quiet or still, which is also where English tranquil comes from. Add the verb ending -izar (like -ize) and you get to make tranquil: to calm someone, or to sedate them. Tranquilízate means calm down.