If someone is grumpy, they are in a bad mood and easily annoyed. Small things bother them. They may look sour, speak shortly, or complain about nothing much. It is informal, common, and a little homely — milder and more everyday than “bad-tempered” in a serious sense. A famous picture is the “grumpy old man,” helped by the dwarf named Grumpy in Snow White, so learners sometimes think the word only fits old men. Anyone can be grumpy: a tired child, a hungry teenager, you on a Monday. It can also be a light noun for a person who is often like this (“He’s an old grump”), but the usual word is the adjective.