deadening vs tedious

deadening is a noun but tedious is not a noun.

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

As adjectives, deadening and tedious are synonyms defined as:

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

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

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

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