From Discworld & Terry Pratchett Wiki

There are an accepted consensus number of seven deadly sins on Roundworld. Early attempts at writing the Wiki pages for Tubso and Bissonomy took it as read that the 7a Virtues outnumbered seven sins by one...

"It doesn't matter that seven-and-one Virtues outnumber the Seven Deadly Sins by one. In Ankh-Morpork, which gang do you think is going to win?"





Breaking News:

Research into this issue has perhaps rendered this statement obsolete. A field researcher has made it back from Ankh-Morpork, poor, yes, but more or less still all there mentally and physically, to report that the street in between Turnwise Broad Way and the Unseen University Backs is called....wait for it... Eight Deadly Sins.

This would suggest - if we set aside the interesting subject of how the street got its name in the first place - that just as the Disc has two-to-the-power-of-three Virtues, it also has sixteen-divided-by-two Deadly Sins. This implies Ankh-Morpork is so lost in sin and degenerate that the City has actually invented an additional two-times fourth Deadly Sin, all of its own.

What could this Sin be? Could she even be forgotten and propping up the bar with Tubso and Bissonomy, bemoaning the good old days?

This interesting street, running parallel to Peach Pie Street and the Street of Alchemists, is not named on The Streets of Ankh-Morpork and is left blank. Eight Deadly Sins is named as a city street in the larger-scale map appearing on the endpapers of The Discworld Companion.

Annotation

There are seven deadly sins which have been known and classified since antiquity. Anger, Envy, Gluttony, Greed, Lust, Pride, and Sloth. It is thought that seven were picked because it made a sacred number and harmoniously balanced the concept of seven opposed Virtues/Graces.

However, the Eastern Orthodox Church breaks with the Western tradition by adding an official Eighth Deadly Sin: Despair.

And apparently, when the Western Church trimmed the list to seven to fit in with its numerology, Despair was dropped to the subs' bench. So is this the former Deadly Sin who shares a bottle with Tubso in the really depressing sort of bar where Death goes, just for the atmosphere?