lap vs lap up

lap is a noun but lap up is not a noun.

Word	Noun	Adjective	Verb	Adverb
lap	Yes	No	Yes	No
lap up	No	No	Yes	No

As verbs, lap and lap up are synonyms defined as:

Other synonyms of lap include lick.

lap (noun)	lap up (noun)
touching with the tongue
movement once around a course
a flap that lies over another part
the part of a piece of clothing that covers the thighs
the upper side of the thighs of a seated person
an area of control or responsibility

lap (verb)	lap up (verb)
wash or flow against	take up with the tongue
take up with the tongue
pass the tongue over
move with or cause to move with a whistling or hissing sound
lie partly over or alongside of something or of one another