sustain vs break down

sustain and break down both are verbs.

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

As verbs, break down is a hyponym of sustain; that is, break down is a word with a more specific, narrower meaning than sustain:

Other hyponyms of sustain include collapse, cramp, break up, collapse, crack, crack up, crock up, stress.

sustain (verb)	break down (verb)
undergo (as of injuries and illnesses)	collapse due to fatigue, an illness, or a sudden attack
establish or strengthen as with new evidence or facts	stop operating or functioning
admit as valid	separate (substances) into constituent elements or parts
supply with necessities and support	make a mathematical, chemical, or grammatical analysis of; break down into components or essential features
provide with nourishment	make ineffective
be the physical support of; carry the weight of	cause to fall or collapse
lengthen or extend in duration or space	lose control of one's emotions
	fall apart