vicious 1. adj. cruel or violent.
viscous 1. adj. gluey, thick, slow moving (used to describe liquids).
Words in the Wild: The vicious baker punished her misshapen gingerbread people by drowning them in sweet, viscous icing.
When I edit, I sometimes see these words standing in for one another, often to comic effect. I now know that one must watch out for cruel glue as well as gooey serial killers. These words look very similar on the page, and autocorrect has no idea, of course, which one is correct in a given situation. This is another tricky pair you’ll want to keep an eye on.
Still vexed? You can find a complete list of the Word Blog’s lexical vexations here.