senseless vs senselessness

senseless is not a noun while senselessness is a noun.

Word	Noun	Adjective	Verb	Adverb
senseless	No	Yes	No	No
senselessness	Yes	No	No	No

senseless (noun)	senselessness (noun)
	total lack of meaning or ideas

senseless (adjective)	senselessness (adjective)
(of especially persons) lacking sense or understanding or judgment
unresponsive to stimulation
not marked by the use of reason
serving no useful purpose; having no excuse for being