To disdain or look down on someone/something; to belittle or make light of (transitive).
敵を侮ってはいけない。
You must not underestimate the enemy.
彼は若さを侮られ、重要な仕事を任されなかった。
He was looked down on because of his youth and wasn't given important work.
相手の実力を侮ると痛い目に遭う。
If you underestimate your opponent's ability, you'll pay for it.
人を侮る言い方は礼儀に反する。
Speaking in a way that belittles others is against good manners.