Buddhism vs Tantra

Buddhism and Tantra both are nouns.

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

As nouns, Tantra is a hyponym of Buddhism; that is, Tantra 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
Tantra: doctrine of enlightenment as the realization of the oneness of one's self and the visible world; combines elements of Hinduism and paganism including magical and mystical elements like mantras and mudras and erotic rites; especially influential in Tibet

Buddhism (noun)	Tantra (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	doctrine of enlightenment as the realization of the oneness of one's self and the visible world; combines elements of Hinduism and paganism including magical and mystical elements like mantras and mudras and erotic rites; especially influential in Tibet
a religion represented by the many groups (especially in Asia) that profess various forms of the Buddhist doctrine and that venerate Buddha