Noun

1. A period of calm weather
2. An untroubled state; free from disturbances
3. The absence of sound
4. A disposition free from stress or emotion

Adjective

1. Characterized by an absence or near absence of agitation or activity
2. Free of noise or uproar; or making little if any sound
3. Of the sun characterized by a low level of surface phenomena like sunspots e.g.

Verb

1. Become quiet or quieter
2. Make calm or still

Adverb

1. With little or no activity or no agitation (`quiet' is a nonstandard variant for `quietly')