bear down vs burden

bear down is not a noun while burden is a noun.

Word	Noun	Adjective	Verb	Adverb
bear down	No	No	Yes	No
burden	Yes	No	Yes	No

As verbs, burden is a hypernym of bear down; that is, burden is a word with a broader meaning than bear down:

Other hypernyms of bear down include charge, saddle.

bear down (noun)	burden (noun)
	weight to be borne or conveyed
	the central idea that is expanded in a document or discourse
	an onerous or difficult concern
	the central meaning or theme of a speech or literary work

bear down (verb)	burden (verb)
exert a force or cause a strain upon	impose a task upon, assign a responsibility to
pay special attention to	weight down with a load
exert full strength
to make a rush at or sudden attack upon, as in battle
exert a force with a heavy weight
contract the abdominal muscles during childbirth to ease delivery