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 this reading yet, so here's a mnemonic to help you:
Think of a man who is cruel. Doesn't matter who, but pick one that you know of that is actually cruel. He can be a real person or someone in a movie or on TV. What does this man do? He do (ひど) cruel things.
All of the food she made tasted awful.
How can you say such a cruel thing to your own girlfriend?
If I had known the heat would be this severe, I wouldn't have moved to this country.