When a teenage boy is not yet man enough to grow a full beard, but instead grows ugly/nasty stubble under the chin and above the throat.
Tyler rubbed his under beard making a loud scratching sound.
Facial hair that grows on the underside of the chin. This style of beard is frequently sported by the overweight, in which case it technically resides on their second chin.
"Kids, take a page from the Underbeard King and get rid of your neckal hair,
`cause you're lookin' like Chewbacca did a face-plant into Nair."
~ excerpt from the traditional Ballad Of The Underbeard
The ungroomed pubic hair of a man. See also "noseless under-beard."
Paul was swimming when his suit was pulled down, revealing to all of us his barbaric under-beard.
the secret for quiz bowl success.
We would have never won that tournament if it weren't for that underbeard.
Pubis hair (those around and above the vagina)
Horny pop babe flashes nice bit of underbeard.