na-adjective, noun
abnormal; unusual; extraordinary
Broadly used for anything deviating from normal, expected, or standard conditions. Can describe physical states, behavior, weather, machinery, etc. Often carries a negative or alarming nuance, but can be neutral in technical contexts.
Antonyms: 正常
今年の夏は異常に暑い。
This summer is abnormally hot.
エンジンに異常は見つからなかった。
No abnormality was found in the engine.
彼の行動は少し異常だと思う。
I think his behavior is a little unusual.