join vs disjoin

join is a noun but disjoin is not a noun.

Word	Noun	Adjective	Verb	Adverb
join	Yes	No	Yes	No
disjoin	No	No	Yes	No

join (noun)	disjoin (noun)
a set containing all and only the members of two or more given sets
the shape or manner in which things come together and a connection is made

join (verb)	disjoin (verb)
make contact or come together	become separated, disconnected or disjoint
cause to become joined or linked	make disjoint, separated, or disconnected; undo the joining of
become part of; become a member of a group or organization
come into the company of
be or become joined or united or linked