missionary work vs mission

missionary work and mission both are nouns.

Word	Noun	Adjective	Verb	Adverb
missionary work	Yes	No	No	No
mission	Yes	No	No	No

As nouns, missionary work and mission are synonyms defined as:

missionary work and mission: the organized work of a religious missionary

missionary work (noun)	mission (noun)
the organized work of a religious missionary	a special assignment that is given to a person or group
	an operation that is assigned by a higher headquarters
	the organized work of a religious missionary
	a group of representatives or delegates
	an organization of missionaries in a foreign land sent to carry on religious work