predisposition; inclination; nature; tendency
Archaic noun for one's innate disposition or habitual tendency. In modern Japanese, 性癖 or 傾向 are more common.
In classical texts, 心癖 is sometimes used to describe a person's innate nature.
Compound of 心 (こころ, heart/mind) and 癖 (くせ, habit/tendency). The exact historical derivation is uncertain, but it likely referred to an ingrained mental habit or natural disposition.