abnormal mentality; abnormal psychology
Refers to a mental state or psychological condition that deviates from the norm. Often used in clinical or descriptive contexts.
His behavior might be a manifestation of an abnormal mentality.
Similar in meaning, but 異常心理 is more commonly used in modern clinical psychology to refer to abnormal psychology as a field of study.
Compound of 変態 (hentai, 'abnormal, transformation') and 心理 (shinri, 'psychology, mental state'). The exact historical derivation is uncertain; the term is conventionally associated with the concept of abnormal mental states.