A short-tempered person gets angry fast. A small thing — a late bus, a noisy room, a slow computer — is enough. It is about how quickly the anger comes, not about being unkind all day. We all know someone like this, and we are sometimes this on a tired day. Though actually, it describes a habit of the temper: they are like this often, not just once. One angry afternoon does not make you short-tempered. Temper here is not the weather's temperature; it is your inner weather — how soon you explode. The noun is a short temper: she has a short temper. The adjective adds -ed: short-tempered. It is not a swear word, but it is not a compliment either. Softer cousins are impatient and irritable.