Where did the phrase "deadpool" originate from

It's a word AND an annoying Marvel character.

Dead pool, noun.

1. A dead pool, also known as a death pool, is a game of prediction which involves guessing when someone will die. Sometimes it is a bet where money is involved. The combination of dead or death, and betting pool, refers to such a gambling arrangement.
2. Common in events where death was a possibility i.e. motor sports, motorcycle or car races.
3. A modern application of the word is used as part of a pool to determine when famous celebrities will die.

Deadpool, an annoying Marvel anti-hero

• Wade Wilson is a former test subject of the Weapon X program, an government program/facility which experimented with various biological and mechanized technology in order to create super soldiers. Often called The Merc with a Mouth, Deadpool is horribly disfigured due to a cancer which ravaged his body.
• While partaking of experimental treatments to fight cancer, his provider's staff would take bets on when the next treatment might be his last; i.e. the dead pool. Upon his escape from his confinement, he took the name Deadpool and as he would say, "the rest is history."
• Wilson is, at best, a murderous anti-hero who has been trained to kill and does so with amazing skill. He is wildly unstable mentally and part of his powers are derived from his inability to know what he will do next. It makes predicting him nearly impossible even for trained fighters since his abilities are outside of his conscious control.

• Wade Wilson (Deadpool, right) is a possible homage or unfortunate copy of a DC anti-hero named Slade Wilson (Deathstroke, left) who is also a mercenary of incomparable skill but written far more seriously. It is mostly Deadpool's antics which makes him considerably more popular than Deathstroke, despite their obvious, murderous similarities.

• Deadpool's most annoying feature is his constant breaking of the Fourth wall and speaking about comics, the comic industry, his creators, the state of the world or opining on the people who read comics.
• Deadpool has been a member of X-Force and the Thunderbolts. As a character Deadpool is either beloved or despised by readers, sometime in the same comic. His numbers however appear to have made him a best seller and thus his continued comic existence and now a possible movie deal.