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 scorn, so the verb version is to scorn and to despise.

Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:

You start to scorn your boss because she's been wearing that same sage suit (さげす) for a month now. She knows you want to wear a sage suit too but you can't wear the same color as her! It's really making you start to despise her. Uhg!