Pathological; relating to disease or an abnormal, unhealthy condition. Often used as '病的な...' to describe morbid or extreme behavior/traits.
彼は病的なまでに整理整頓にこだわる。
He is obsessively tidy to an unhealthy extent.
その症例は病的な変化が見られたため、さらに検査を行った。
Because pathological changes were observed in that case, further tests were performed.
病的な嫉妬心は人間関係を壊すことがある。
Morbid jealousy can sometimes ruin relationships.