Real Dictionary

citrus
A citrus fruit is a juicy fruit with a sharp taste such as an orange, lemon, or grapefruit.

citrus in American English
any of a genus (Citrus) of trees and shrubs of the rue family, that bear oranges, lemons, limes, or other such fruit
of these trees and shrubs
adjective: of or pertaining to such trees or shrubs, or their fruit
noun: any small tree or spiny shrub of the genus Citrus, of the rue family, including the lemon, lime, orange, tangerine, grapefruit, citron, kumquat, and shaddock, widely cultivated for fruit or grown as an ornamental

citrus in British English
adjective: of, relating to, or belonging to the genus Citrus or to the fruits of plants of this genus
noun: any tree or shrub of the tropical and subtropical rutaceous genus Citrus, which includes the orange, lemon, lime, grapefruit, citron, and calamondin