Barleycorn \Bar"ley*corn`\, n. [See Corn.]

1. A grain or ``corn'' of barley.

2. Formerly, a measure of length, equal to the average length of a grain of barley; the third part of an inch.

John Barleycorn, a humorous personification of barley as the source of malt liquor or whisky.

Source: Webster's Revised Unabridged Dictionary (1913)