1.Lit. [for a horse] to pull back and up onto its hind legs in an effort to move backwards rapidly or throw a rider. (See also rear up.) The animal reared back in terror.The horse reared back and almost threw its rider.
2.Fig. [for a person] to pull back and stand up or sit up straighter. He reared back in his chair and looked perturbed.Tom reared back in his chair, waiting for something else to happen.