What is the meaning of Lemon?

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 C. Limonum or C. Medica (var. Limonum). There are many varieties of the fruit, some of which are sweet.

Source: Webster’s Revised Unabridged Dictionary (1913), via OPTED