This word is a combination of お腹 (belly) and 空く (to become empty). When your belly becomes empty, you're going to get hungry.

お腹が空く is the most standard expression for saying you're hungry in Japanese. You'll typically use it in the past tense, like お腹が空いた. In conversation, it's common to drop the が, so you'll also hear people say things like お腹空いた！ when they're out with friends or family and want to grab a bite to eat. Note that it's often written in kana, either fully or partly, like お腹がすく.

お腹 uses the reading you learned with the vocabulary, but 空く is actually going to use a new reading here: すく. Here's a mnemonic to help you remember it:

When you start to get hungry, you threaten to sue (す) the people around you for not feeding you. Some people just get hangry, but you get full-on litigious. You've threatened to sue your friends so many times now that they all habitually carry granola bars and trail mix to keep you from getting even the slightest bit peckish.