Yes, quiet is a Scrabble word!

Adverb

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

Verb

1. Become quiet or quieter

2. Make calm or still

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. Not showy or obtrusive

4. In a softened tone

5. (of a body of water) free from disturbance by heavy waves

6. Of the sun characterized by a low level of surface phenomena like sunspots e.g.

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