What is "citrus limonum"

Lemon \Lem"on\ (l[e^]m"[u^]n), n. [F. limon, Per. l[imac]m[=u]n; cf. Ar. laim[=u]n, Sp. limon, It. limone. Cf. Lime a fruit.]

1. (Bot.) An oval or roundish fruit resembling the orange, and containing a pulp usually intensely acid. It is produced by a tropical tree of the genus Citrus, the common fruit known in commerce being that of the species Citrus Limonum or Citrus Medica (var. Limonum). There are many varieties of the fruit, some of which are sweet.

2. The tree which bears lemons; the lemon tree.

   Lemon grass (Bot.), a fragrant East Indian grass ( Andropogon Sh[oe]nanthus, and perhaps other allied species), which yields the grass oil used in perfumery.

   Lemon sole (Zo["o]l.), a yellow European sole ( Solea aurantiaca).

   Salts of lemon (Chem.), a white crystalline substance, inappropriately named, as it consists of an acid potassium oxalate and contains no citric acid, which is the characteristic acid of lemon; -- called also salts of sorrel. It is used in removing ink stains. See Oxalic acid, under Oxalic. [Colloq.]