quiet vs quieten

quiet is a noun but quieten is not a noun.

Word	Noun	Adjective	Verb	Adverb
quiet	Yes	Yes	Yes	Yes
quieten	No	No	Yes	No

As verbs, quiet and quieten are synonyms defined as:

Other synonyms of quiet include calm, calm down, lull, still, tranquilize, tranquillise, tranquillize.

As verbs, quiet and quieten are synonyms defined as:

Other synonyms of quiet include hush, pipe down, quiesce, quiet down.

quiet (noun)	quieten (noun)
a disposition free from stress or emotion
the absence of sound
a period of calm weather
an untroubled state; free from disturbances

quiet (adjective)	quieten (adjective)
free of noise or uproar; or making little if any sound
characterized by an absence or near absence of agitation or activity
(of the sun) characterized by a low level of surface phenomena, such as sunspots
(of a body of water) free from disturbance by heavy waves
in a softened tone
not showy or obtrusive

quiet (adverb)	quieten (adverb)
with little or no activity or no agitation (`quiet' is a nonstandard variant for `quietly')