Since this word has okurigana (hiragana attached to the kanji) you know that it's probably going to be the kun'yomi reading.
The reading comes from 薄い, so if you know that you'll be able to read this too. If not, here's a mnemonic to help you:
You don't want your drink to be diluted, so you sue (うす) anyone who dares pour you a weak drink.
Please don't take this with alcohol as its effectiveness will be diminished.
The pink paint, diluted with water, was left on the palette.
With just one remark, the inherent value of the letter was diminished.