Underboss 

Member of a mafia family, typically directly underneath the Don. Handles the mundane details of running a crime family.

The underboss put the capo in charge of making sure the hit was carried out.

Underboss by Roberto Manchez December 29, 2004

Underoos 

A nickname or name for undergarments that are tight, similar to that of spandex. Also used as a nickname from Tony Stark to Peter Parker in Captain America Civil War.

Tony Stark: "Alright, I've run out of patience, UNDEROOS!" Peter Parker (Spider-Man) flips in.

Underoos by Peterparkerfanfic October 1, 2017

raving underpass

The act of dancing underneath a concrete structure, to any given beat. Usual participants are gothic warriors and princesses.

Buddy and Joe were raving underpass I-95 over the weekend.

raving underpass by WebstersBest June 8, 2016

Underbus

Verb used to describe the act of "throwing someone under the bus" or otherwise admitting someone's wrongdoing for them.

My sister was in trouble with my mom, so she underbussed me for something I did last week, and got herself off the hook.
An underbusser is a grown tattletale.

Underbus by misshappenstanc October 9, 2017

underboob 

cleavage visible from the part of the shirt that covers the bottom of the female breasts

If that is not a deliberate underboob, I don't know what is.

underboob by The Return of Light Joker March 20, 2009

Undernose 

The act of placing a COVID mask under one's nose to facilitate easier breathing by completely defeating the purpose of wearing it at all.

Example: "I told this lady at work to put a mask on but she undernosed it so I walked away."

Undernose by Milk Lunch June 23, 2020

underboobage 

The southern hemisphere of a woman's breasts, as often displayed to the delight of virile men.

I love to see the underboobage of buxom females playing volleyball in the sand, especially whilst wearing all-too-short crop tops. Oh yeah, neathage!

underboobage by noahb555 September 10, 2010