to relax /rɪˈlæks/ /rɪˈlæks/
to rest /rest/ /rest/
to repose /rɪˈpoʊz/ /rɪˈpəʊz/
to calm down /kɑm daʊn/ /kɑːm daʊn/
to calm /kɑm/ /kɑm/
to settle down /ˈsɛtəl daʊn/ /ˈsɛtl daʊn/
to become tranquil and quiet