Linch'pin, n.

noun

n. [A-S. lynis, the axle-tree, D. luns, lens, O. L. Ger. lunisa, lünse, L. Ger. lunse, H. Ger. lünse, from O. L. Ger. & O. H. Ger. lun, peg, bolt.] A pin used to prevent the wheel of a carriage from sliding off the axle-tree.