IPA: /ˈjɔːnər/
KK: /ˈjɔːnər/
A person who yawns or something that is boring and makes people yawn.
The movie was such a yawner that many people fell asleep in the theater.
Yawner → The word is formed from "yawn" (of uncertain origin, possibly imitative of the sound made during yawning) and "-er" (meaning a person who). A yawner is a person who yawns, typically indicating tiredness or boredom.
Think of someone who is making the sound of a yawn — that's why a yawner is a person who yawns.