1.  barley(n = noun.food) barleycorn - a grain of barley;
is a kind of cereal, food grain, grain
is a part of common barley, hordeum vulgare
has particulars: pearl barley

2.  barley(n = noun.plant) - cultivated since prehistoric times; grown for forage and grain;
is a kind of cereal, cereal grass
is a member of genus hordeum, hordeum
has particulars: common barley, hordeum vulgare, barley grass, hordeum murinum, wall barley, foxtail barley, hordeum jubatum, squirreltail barley, squirreltail grass, hordeum pusillum, little barley

   A valuable grain, of the family of grasses, genus Hordeum, used for food, and for making malt, from which are prepared beer, ale, and whisky. [1913 Webster]

barley, n.
1 any of various hardy awned cereals of the genus Hordeum widely used as food and in malt liquors and spirits such as whisky.
2 the grain produced from this (cf. pearl barley).

Idiom:
barley sugar an amber-coloured sweet made of boiled sugar, traditionally shaped as a twisted stick. barley water a drink made from water and a boiled barley mixture.

Etymology:
OE b{aelig}rlic (adj.) f. b{aelig}re, bere barley

barley candy, barley grass, barley water, common barley, foxtail barley, little barley, pearl barley, squirreltail barley, wall barley