behavior vs demeanour

behavior and demeanour both are nouns.

Word	Noun	Adjective	Verb	Adverb
behavior	Yes	No	No	No
demeanour	Yes	No	No	No

As nouns, behavior and demeanour are synonyms defined as:

behavior and demeanour: (behavioral attributes) the way a person behaves toward other people

Other synonyms of behavior include behaviour, conduct, demeanor, deportment.

behavior (noun)	demeanour (noun)
manner of acting or controlling yourself	(behavioral attributes) the way a person behaves toward other people
(psychology) the aggregate of the responses or reactions or movements made by an organism in any situation
(behavioral attributes) the way a person behaves toward other people
the action or reaction of something (as a machine or substance) under specified circumstances