This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb.

The kanji itself means pain, and this verb is transitive, so it means to inflict pain. In other words, it's to injure something or to hurt someone.

This verb focusses on the pain involved in an injury, so it can only be used for things that feel pain, like people and body parts.