1.
If you wear something down or if it wears down, it becomes flatter or smoother as a result of constantly rubbing against something else.
Pipe smokers sometimes ~ the tips of their teeth where they grip their pipes...
The machines start to ~, they don’t make as many nuts and bolts as they used to...
Elephants wear the tusk down faster than they can grow it.
PHRASAL VERB: V P n (not pron), V P, V n P
2.
If you wear someone down, you make them gradually weaker or less determined until they eventually do what you want.
They hoped the waiting and the uncertainty would ~ my resistance...
He believed that he could wear her down if he only asked often enough.
PHRASAL VERB: V P n (not pron), V n P