Proto-Indo-European root meaning "to join."
It forms all or part of: adjoin; adjust; conjoin; conjugal; conjugate; conjugation; conjunct; disjointed; enjoin; injunction; jugular; jostle; joust; join; joinder; joint; jointure; junction; juncture; junta; juxtapose; juxtaposition; rejoin (v.2) "to answer;" rejoinder; subjoin; subjugate; subjugation; subjunctive; syzygy; yoga; yoke; zeugma; zygoma; zygomatic; zygote.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit yugam "yoke," yunjati "binds, harnesses," yogah "union;" Hittite yugan "yoke;" Greek zygon "yoke," zeugnyanai "to join, unite;" Latin iungere "to join," iugum "yoke;" Old Church Slavonic igo, Old Welsh iou "yoke;" Lithuanian jungas "yoke," jungti "to fasten to a yoke;" Old English geoc "yoke."
1888 in yoga sense "a spiritual center of power in the human body," from Sanskrit cakra "circle, wheel," from PIE root *kwel- (1) "revolve, move round."
"intense esoteric meditation through yoga," 1827, earlier "state of union with creation" (1795), from Sanskrit samadhi-, literally "a putting or joining together," from sam- "together" (from PIE root *sem- (1) "one; as one, together with") + a- "toward" + stem of dadhati "puts, places" (from PIE root *dhe- "to set, put").
1808, "that part of the Vedas which contains hymns," from Sanskrit mantra-s "sacred message or text, charm, spell, counsel," literally "instrument of thought," related to manyate "thinks," from PIE root *men- (1) "to think." Meaning "sacred text used as a charm or incantation" is by 1900; sense of "special word used for yoga meditation" is recorded in English by 1956.