bolt [OE] In Old English bolt meant ‘an arrow’. To have shot your bolt [L16th], ‘be able to do no more’, is taken from archery. The completely unexpected bolt from the blue [L19th], on the other hand, is a thunderbolt [LME], a flash of lightning with a simultaneous crash of thunder. Bolt upright [LME] comes from the verb which originally meant ‘to start, to spring’ and is the same verb as ‘to run off’ [L16th] like a horse bolting [E19th]. It goes back to the ‘arrow’ sense of bolt, from the idea of the speed of an arrow shot from a bow.