{To sit under}, to be under the instruction or ministrations of; as, to sit under a preacher; to sit under good preaching. {To sit up}, to rise from, or refrain from, a recumbent posture or from sleep; to sit with the body upright; as, to sit up late at night; also, to watch; as, to sit up with a sick person. ``He that was dead sat up, and began to speak.'' --Luke vii. 15.