thing vs nonessential

thing and nonessential both are nouns.

Word	Noun	Adjective	Verb	Adverb
thing	Yes	No	No	No
nonessential	Yes	Yes	No	No

As nouns, nonessential is a hyponym of thing; that is, nonessential is a word with a more specific, narrower meaning than thing:

thing (noun)	nonessential (noun)
a separate and self-contained entity	anything that is not essential
an action
an artifact
an entity that is not named specifically
any attribute or quality considered as having its own existence
a special abstraction
a special objective
a vaguely specified concern
a statement regarded as an object
an event
a persistent illogical feeling of desire or aversion
a special situation

thing (adjective)	nonessential (adjective)
	not of prime or central importance