This is the usual American spelling of anaemic. As a medical word it means having anemia — the blood is not doing its oxygen-carrying job well, so the person may look pale and feel worn out. People also stretch it: an anemic performance is weak, thin, with little energy or colour, even when nobody is talking about blood. That second use is a little informal, and a little unkind if you aim it at a person. British English uses anaemic. You can also hear the noun an anemic for a person with the condition, but doctors more often say a patient with anemia.