Just saying the word calm reminds you of how it feels to be calm — steady, at rest, not agitated, chilled out, caaaaalllmmmm. Waters without waves? People without drama? Sounds calm.
Some synonyms of the adjective calm are peaceful and even-tempered. As a verb, it describes making someone steady and still — in other words, calm. Taking a walk or calling a friend might help you calm down when you are upset. As a noun, calm is a state of peace or stillness — the calm of your neighborhood at daybreak or the calm you seek when you exercise.