That is subject to or kept under proper control; (of a scientific study) that has an adequate control group (cf. controlled, adj. 2a).

Of a hound: Not easily diverted from the scent. Of a horse: Not nervous, skittish, or excitable; also (cf. A. 4), that travels at a moderate and even…

Having the physical faculties under control. spec. of a horse or its action.

Of persons, their conduct, practices, etc.: Keeping due measure, self-restrained, moderate. Of a horse: Not over-excitable or impetuous.