departure vs deviation

departure and deviation both are nouns.

Word	Noun	Adjective	Verb	Adverb
departure	Yes	No	No	No
deviation	Yes	No	No	No

As nouns, departure and deviation are synonyms defined as:

departure and deviation: a variation that deviates from the standard or norm

Other synonyms of departure include difference, divergence.

departure (noun)	deviation (noun)
the act of departing	deviate behavior
euphemistic expressions for death	a turning aside (of your course or attention or concern)
a variation that deviates from the standard or norm	the error of a compass due to local magnetic disturbances
	the difference between an observed value and the expected value of a variable or function
	a variation that deviates from the standard or norm