Wearisome means causing you to feel tired, bored, or worn down, not from physical exhaustion but from being tedious, repetitive, or dragging on too long. A wearisome task might be copying the same math problem 100 times, not because it's hard, but because it's so repetitive that your mind goes numb. A wearisome speech is one that drones on and on until everyone in the audience is fighting to keep their eyes open.

The word captures that special kind of tiredness that comes from monotony or being stuck doing something dull. Reading the same book for the twentieth time might be wearisome, even if you enjoyed it the first few times. Listening to someone complain about the same thing over and over becomes wearisome after a while, no matter how patient you try to be.

Notice that wearisome describes the thing itself (the boring lecture, the repetitive chore), while weary describes how you feel afterward. After a wearisome day of tedious errands, you might feel weary and ready for something more interesting.