Buddhism vs Theravada

Buddhism and Theravada both are nouns.

Word	Noun	Adjective	Verb	Adverb
Buddhism	Yes	No	No	No
Theravada	Yes	No	No	No

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

Buddhism: the teaching of Buddha that life is permeated with suffering caused by desire, that suffering ceases when desire ceases, and that enlightenment obtained through right conduct and wisdom and meditation releases one from desire and suffering and rebirth
Theravada: one of two great schools of Buddhist doctrine emphasizing personal salvation through your own efforts; a conservative form of Buddhism that adheres to Pali scriptures and the non-theistic ideal of self purification to nirvana; the dominant religion of Sri Lanka (Ceylon) and Myanmar (Burma) and Thailand and Laos and Cambodia

Buddhism (noun)	Theravada (noun)
the teaching of Buddha that life is permeated with suffering caused by desire, that suffering ceases when desire ceases, and that enlightenment obtained through right conduct and wisdom and meditation releases one from desire and suffering and rebirth	one of two great schools of Buddhist doctrine emphasizing personal salvation through your own efforts; a conservative form of Buddhism that adheres to Pali scriptures and the non-theistic ideal of self purification to nirvana; the dominant religion of Sri Lanka (Ceylon) and Myanmar (Burma) and Thailand and Laos and Cambodia
a religion represented by the many groups (especially in Asia) that profess various forms of the Buddhist doctrine and that venerate Buddha