tantra (n.)

type of Hindu religious book, 1799, from Sanskrit tantram, literally "loom, warp," hence, figuratively, "groundwork, system, doctrine," from tan "to stretch, extend," from PIE root *ten- "to stretch."

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Definitions of tantra from WordNet
tantra (n.)
any of a fairly recent class of Hindu or Buddhist religious literature concerned with ritual acts of body and speech and mind;
Tantra (n.)
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;
Synonyms: Tantrism