assignment vs co-option

assignment and co-option both are nouns.

Word	Noun	Adjective	Verb	Adverb
assignment	Yes	No	No	No
co-option	Yes	No	No	No

As nouns, co-option is a hyponym of assignment; that is, co-option is a word with a more specific, narrower meaning than assignment:

assignment: the act of putting a person into a non-elective position
co-option: the act of appointing summarily (with or without the appointee's consent)

Other hyponyms of assignment include nomination, co-optation, delegacy, ordinance, ordination, recognition.

assignment (noun)	co-option (noun)
a duty that you are assigned to perform (especially in the armed forces)	the selection of a new member (usually by a vote of the existing membership)
the act of putting a person into a non-elective position	the act of appointing summarily (with or without the appointee's consent)
the act of distributing something to designated places or persons
an undertaking that you have been assigned to do (as by an instructor)
the instrument by which a claim or right or interest or property is transferred from one person to another
(law) a transfer of property by deed of conveyance