Here's where it gets crazy, y'all. I look up the word dextrous this morning and loandbehold! not only does it exist, but it's spelled and pronounced exactly like I thought it would be... what are the odds?! But then I tried to look up my trusted friend dexterious (which I thought was the alternate spelling) only to find that it does not exist. Egads! Instead there's this random concoctification called dexterous. And that is the world from which dextrous springs and which is a synonym thereunto. Who knew?
So for everyone's enlightenment here is the entire entry for dextrous from my trusty computer New Oxford American Dictionary: