1680s, agent noun from yawn (v.). Meaning "boring thing" is 1942, American English colloquial (yawn (n.) in this sense is attested from 1889).
yarn
yarrow
yaw
yawl
yawn
yawner
yawp
yaws
yay
yclept
ye
)window.location='https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=byronic106@yahoo.com&lc=US&item_name=Donation+to +Help+Keep+Etymonline+Free+and+Open&no_note=0&cn=&curency_code=USD&bn=PP-DonationsBF:btn_donateCC_LG.gif:NonHosted'){kind=link}