Webster’s Revised Unabridged Dictionary · 1913
Barleycorn
Bar′ley·corn′ (·kôrn′), 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.