Mine-roof prop

• A wooden prop used to support the roof of a mine
• Mine support
• Miner's roof prop
• Mine roof prop
• Wedge stuck under a wheel
• A chock or bar wedged under a wheel or between the spokes to prevent a vehicle from rolling down an incline

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Sprag \Sprag\, v. t. [imp. & p. p. Spragged (spr[a^]gd); p. pr. & vb. n. Spragging (-g[i^]ng).] To check the motion of, as a carriage on a steep grade, by putting a sprag between the spokes of the wheel. --R. S. Poole. To prop or sustain with a sprag.

Wiktionary Word definitions in Wiktionary
Etymology 1 (alternative form of sprack English) Etymology 2 n. A billet of wood; a piece of timber, a similar solid object or constructed unit used as a prop. v 1 (context transitive English) To check the motion of, as a carriage on a steep slope, by putting ...

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
"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 .