activity vs eructation

activity and eructation both are nouns.

Word	Noun	Adjective	Verb	Adverb
activity	Yes	No	No	No
eructation	Yes	No	No	No

As nouns, eructation is a hyponym of activity; that is, eructation is a word with a more specific, narrower meaning than activity:

activity: the state of being active
eructation: (of volcanoes) pouring out fumes or lava (or a deposit so formed)

Other hyponyms of activity include agency, busyness, hum, behavior, behaviour, eruption, extravasation, operation, overdrive, play, swing.

activity (noun)	eructation (noun)
any specific behavior	a reflex that expels gas noisily from the stomach through the mouth
the trait of being active; moving or acting rapidly and energetically	(of volcanoes) pouring out fumes or lava (or a deposit so formed)
an organic process that takes place in the body
a process existing in or produced by nature (rather than by the intent of human beings)
the state of being active
(chemistry) the capacity of a substance to take part in a chemical reaction