summons vs summon

summons is a noun but summon is not a noun.

Word	Noun	Adjective	Verb	Adverb
summons	Yes	No	Yes	No
summon	No	No	Yes	No

As verbs, summons and summon are synonyms defined as:

Other synonyms of summons include cite.

summons (noun)	summon (noun)
a writ issued by authority of law; usually compels the defendant's attendance in a civil suit; failure to appear results in a default judgment against the defendant
a request to be present
an order to appear in person at a given place and time

summons (verb)	summon (verb)
call in an official matter, such as to attend court	make ready for action or use
	call in an official matter, such as to attend court
	ask to come
	gather or bring together
	cause to become available for use, either literally or figuratively