c. 1300, yenen, yonen, from Old English ginian, gionian "open the mouth wide, yawn, gape," from Proto-Germanic *gin- (source also of Old English giwian, giowian, giwan "to request," Old Norse gina "to yawn," Dutch geeuwen, Old High German ginen"to be wide open," German gähnen "to yawn"), from PIE root *ghieh- "to yawn, gape, be wide open." Modern spelling is from 16c. Related: Yawned; yawning.
*yē-, Proto-Indo-European root meaning "to throw, impel."
It forms all or part of: abject; abjection; adjacence; adjacent; adjective; aphetic; catheter; circumjacent; conjecture; deject; ease; ejaculate; eject; enema; gist; ictus; interjacent; inject; interject; interjection; jess; jet (v.1) "to sprout or spurt forth, shoot out;" jet (n.1) "stream of water;" jete; jetsam; jettison; jetton; jetty (n.) "pier;" joist; jut; object; objection; objective; paresis; project; projectile; reject; rejection; subjacent; subject; subjective; trajectory.
It is the hypothetical source of/evidence for its existence is provided by: Hittite ijami "I make;" Latin iacere "to throw, cast."