Something vexatious, pronounced "veks-AY-shus," is irritating or annoying, like an itch in the middle of your back that you can't reach, or a task that you need to do for work. You can also describe something that's worrying you as vexatious, like a parent's vexatious thoughts the first time a child drives the car alone. Vexatious is also a legal term. It describes a lawsuit meant to annoy, with no hope of winning the suit.