yawn v.

Proto-Indo-European root meaning "to yawn, gape, be wide open." 

It forms all or part of: chaos; chasm; dehiscence; gap; gasp; gawp; hiatus; yawn.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vijihite "to gape, be ajar;" Greek khainein, Latin hiare "to yawn, gape;" Old Church Slavonic zinoti "to open (one's mouth);" Russian razinut', Serbo-Croatian zinuti, Lithuanian žioju, žioti, Czech zivati "to yawn;" Old English ginian, gionian "open the mouth wide, yawn, gape," Old Norse gina "to yawn," Dutch geeuwen, Old High German ginen "to be wide open," German gähnen "to yawn."

"a gaping," in botany, "the discharge of seeds or pollen," 1828, from Modern Latin dehiscentia, from dehiscentem (nominative dehiscens), present participle of dehiscere "to gape, open, split down" (of the earth, etc.), from de- (see de-) + hiscere, inchoative of hiare "to yawn" (see yawn (v.)). Related: Dehisce (1650s); dehiscent (1640s).

1680s, agent noun from yawn (v.). Meaning "boring thing" is 1942, American English colloquial (yawn (n.) in this sense is attested from 1889).