tedious vs deadening

tedious is not a noun while deadening is a noun.

Word	Noun	Adjective	Verb	Adverb
tedious	No	Yes	No	No
deadening	Yes	Yes	No	No

As adjectives, tedious and deadening are synonyms defined as:

tedious and deadening: so lacking in interest as to cause mental weariness

Other synonyms of tedious include boring, dull, ho-hum, irksome, slow, tiresome, wearisome.

tedious (noun)	deadening (noun)
	the act of making something futile and useless (as by routine)

tedious (adjective)	deadening (adjective)
using or containing too many words	so lacking in interest as to cause mental weariness
so lacking in interest as to cause mental weariness