incident vs to-do

incident and to-do both are nouns.

Word	Noun	Adjective	Verb	Adverb
incident	Yes	Yes	No	No
to-do	Yes	No	No	No

As nouns, to-do is a hypernym of incident; that is, to-do is a word with a broader meaning than incident:

Other hypernyms of incident include commotion, disruption, disturbance, flutter, hoo-ha, hoo-hah, hurly burly, kerfuffle.

incident (noun)	to-do (noun)
a single distinct event	a disorderly outburst or tumult
a public disturbance

incident (adjective)	to-do (adjective)
(sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence
falling or striking of light rays on something