monotonous vs dull

monotonous and dull both are adjectives.

Word	Noun	Adjective	Verb	Adverb
monotonous	No	Yes	No	No
dull	No	Yes	Yes	No

monotonous (adjective)	dull (adjective)
tediously repetitious or lacking in variety	not having a sharp edge or point
sounded or spoken in a tone unvarying in pitch	emitting or reflecting very little light
	lacking in liveliness or animation
	not keenly felt
	darkened with overcast
	(of business) not active or brisk
	blunted in responsiveness or sensibility
	being or made softer or less loud or clear
	slow to learn or understand; lacking intellectual acuity
	not clear and resonant; sounding as if striking with or against something relatively soft
	(of color) very low in saturation; highly diluted
	so lacking in interest as to cause mental weariness

monotonous (verb)	dull (verb)
	become dull or lusterless in appearance; lose shine or brightness
	make less lively or vigorous
	become less interesting or attractive
	make dull in appearance
	make dull or blunt
	deaden (a sound or noise), especially by wrapping
	make numb or insensitive