My internet research has revealed the fact that there actually is, rather ironically, a Cardinal Sin, but aside from that I can’t find out what a “cardinal sin” is. It’s a phrase I found myself using today, ex, “It’s not like it’s a cardinal sin.” The origins of the phrase would be rather interesting as well.
A “Cardinal” sin is a serious offense, the likes of which can send you to hell if you die without confessing it. It’s the opposite of a “Venial” sin, which is trivial and of little consequence. I seldom hear either term since leaving Catholic school.
No, that’s a “mortal” sin.
There are seven “cardinal” sins, also known as the “deadly sins.” They are pride, covetousness, lust, anger, gluttony, envy, and sloth. They are the basic sins from which all others originate.
Thanks for the prompt reply. I updated the Wikipedia article appropriately.
And each cardinal sin has an accompaning cardinal virtue…humility, liberality, chastity, patience, abstinence, kindness, and dilligence.
Of course, there’s also Cardinal Sin. 
Poly, you never cease to amaze Me!!
Check out deadlysins.com for more information. Each of the cardinal sins is associated with a contrary virtue, an animal, and a punishment.
Not to be confused with 7deadlysims.com
But is there a Cardinal Biggles?
Don’t suppose you checked the link in the OP? :dubious:
An error by a St. Louis ballplayer.
As far as we Catholics are concerned, the cardinal sins are not really sins at all. rather, they are the things which lead to sin. In other words, if you feel these emotion/get into these states, you’re heading for trouble and need to reconsider yourself. But each of them is, on some level, quite natural, albeit not desirable. And one of them, “Pride”, can also actually be a virtue. Such is the way of the world.