die vs break down

die is a noun but break down is not a noun.

Word	Noun	Adjective	Verb	Adverb
die	Yes	No	Yes	No
break down	No	No	Yes	No

As verbs, die and break down are synonyms defined as:

Other synonyms of die include break, conk out, fail, give out, give way, go, go bad.

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

die: be brought to or as if to the point of death by an intense emotion such as embarrassment, amusement, or shame
break down: lose control of one's emotions

Other hypernyms of die include lose it, snap.

die (noun)	break down (noun)
a small cube with 1 to 6 spots on the six faces; used in gambling to generate random numbers
a device used for shaping metal
a cutting tool that is fitted into a diestock and used for cutting male (external) screw threads on screws or bolts or pipes or rods

die (verb)	break down (verb)
pass from physical life and lose all bodily attributes and functions necessary to sustain life	collapse due to fatigue, an illness, or a sudden attack
disappear or come to an end	stop operating or functioning
suffer spiritual death; be damned (in the religious sense)	separate (substances) into constituent elements or parts
stop operating or functioning	make a mathematical, chemical, or grammatical analysis of; break down into components or essential features
lose sparkle or bouquet	make ineffective
to be on base at the end of an inning, of a player	cause to fall or collapse
cut or shape with a die	lose control of one's emotions
be brought to or as if to the point of death by an intense emotion such as embarrassment, amusement, or shame	fall apart
languish as with love or desire
feel indifferent towards
suffer or face the pain of death