D defs.my
Entry 2 senses Webster, 1913

Barleycorn

· Bar·ley·corn · IPA /ˈbɑː(ɹ)liˌkɔː(ɹ)n/
01 n. A grain or “corn” of barley.
  1. 1.
    A grain or “corn” of barley.
  2. 2.
    Formerly , a measure of length, equal to the average length of a grain of barley; the third part of an inch.
Phrases & compounds
John Barleycorn — a humorous personification of barley as the source of malt liquor or whisky.