chat·e·laine (shăt′l-ān′) n. 1. a. The mistress of a castle. b. The mistress of a large, fashionable household. 2. A clasp or chain worn at the waist for holding keys, a purse, a watch, or other small household items. [French châtelaine, feminine of châtelain, chatelain, from Old French chastelain; see chatelain.] chatelaine (ˈʃætəˌleɪn …