Something that's univocal is so clear that there's only one way to interpret it. A dog that's growling ferociously and baring its teeth is sending a univocal message to keep your distance.
You might also call univocal things "unambiguous." There's no way to misunderstand something that's truly univocal — its meaning is consistent and obvious. Your mom's univocal instruction to be home by 9:00 PM leaves no room for doubt: she means 9:00, not 9:30 or 10:15. This adjective is most often used in linguistics to talk about words, and its Latin roots are uni-, "having only one," and vox, "voice."