sprag, sprag, n. a piece of wood used to lock a wheel: a punch-prop in mining.
Next instant (to make quite sure) I jumped out, ran to the front, and lowered the sprag.
Conclusion; with a testimonial of commodore sprag in behalf of the assembly.
For all that, it's a sheer impossibility that you should guess who put a sprag in the wheel of Hilton's chariot.
"prop in a mine," 1841, of unknown origin. Transferred by 1878 to wood blocks, etc., used to brake motor vehicles. As a verb, from 1841. Related: Spragged; spragging.