'Bolt upright' definitions:

Definition of 'Bolt upright'

From: GCIDE

Bolt \Bolt\, adv. In the manner of a bolt; suddenly; straight; unbendingly. [1913 Webster]
[He] came bolt up against the heavy dragoon. --Thackeray. [1913 Webster]
Bolt upright. (a) Perfectly upright; perpendicular; straight up; unbendingly erect. --Addison. (b) On the back at full length. [Obs.] --Chaucer. [1913 Webster]