pathological
adj.adj. describing a behavior or condition that is extreme, uncontrolled, or caused by a disease. You use it for someone who cannot stop doing something harmful, like lying.
adj. relating to or caused by physical or mental disease; in a behavioral context, compulsive and obsessive. Often used to describe chronic conditions that deviate from a healthy or normal state.
He is a pathological liar who cannot tell the truth.
The doctor ordered more tests to determine if the tissue growth was pathological or benign.
In mathematical analysis, a pathological function is one whose properties are considered exceptionally atypical or counterintuitive, often serving as a counterexample to more general theories.
From pathology + -ical.
Often used to modify nouns related to behavior (liar, gambler) or medical conditions (state, condition).