earthquake vs to-do

earthquake and to-do both are nouns.

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

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

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

earthquake (noun)	to-do (noun)
shaking and vibration at the surface of the earth resulting from underground movement along a fault plane or from volcanic activity	a disorderly outburst or tumult
a disturbance that is extremely disruptive