boil over vs boil

boil over is not a noun while boil is a noun.

Word	Noun	Adjective	Verb	Adverb
boil over	No	No	Yes	No
boil	Yes	No	Yes	No

As verbs, boil is a hypernym of boil over; that is, boil is a word with a broader meaning than boil over:

boil over (noun)	boil (noun)
	the temperature at which a liquid boils at sea level
	a painful sore with a hard core filled with pus

boil over (verb)	boil (verb)
overflow or cause to overflow while boiling	immerse or be immersed in a boiling liquid, often for cooking purposes
	come to the boiling point and change from a liquid to vapor
	bring to, or maintain at, the boiling point
	be in an agitated emotional state
	be agitated