hold on vs grasp

hold on is not a noun while grasp is a noun.

Word	Noun	Adjective	Verb	Adverb
hold on	No	No	Yes	No
grasp	Yes	No	Yes	No

As verbs, hold on and grasp are synonyms defined as:

hold on (noun)	grasp (noun)
	the act of grasping
	an intellectual hold or understanding
	understanding of the nature or meaning or quality or magnitude of something
	the limit of capability

hold on (verb)	grasp (verb)
be persistent, refuse to stop	get the meaning of something
stop and wait, as if awaiting further instructions or developments	hold firmly
hold the phone line open
hold firmly
retain possession of