taper vs lessen

taper is a noun but lessen is not a noun.

Word	Noun	Adjective	Verb	Adverb
taper	Yes	No	Yes	No
lessen	No	No	Yes	No

As verbs, lessen is a hypernym of taper; that is, lessen is a word with a broader meaning than taper:

Other hypernyms of taper include decrease, diminish, fall.

taper (noun)	lessen (noun)
stick of wax with a wick in the middle
a loosely woven cord (in a candle or oil lamp) that draws fuel by capillary action up into the flame
the property possessed by a shape that narrows toward a point (as a wedge or cone)
a convex shape that narrows toward a point

taper (verb)	lessen (verb)
give a point to	decrease in size, extent, or range
diminish gradually	wear off or die down
	make become smaller