drop off vs lessen

drop off and lessen both are verbs.

Word	Noun	Adjective	Verb	Adverb
drop off	No	No	Yes	No
lessen	No	No	Yes	No

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

Other hypernyms of drop off include decrease, diminish, fall.

drop off (verb)	lessen (verb)
change from a waking to a sleeping state	decrease in size, extent, or range
fall to a lower standard	wear off or die down
fall or diminish	make become smaller
retreat
remove (cargo, people, etc.) from and leave