thing vs affair

thing and affair both are nouns.

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

As nouns, thing and affair are synonyms defined as:

Other synonyms of thing include matter.

thing (noun)	affair (noun)
a separate and self-contained entity	a vaguely specified concern
an action	a formal or official social gathering or ceremony of people
an artifact	a usually secretive or illicit sexual relationship
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