"citrus" in the noun sense
1. citrus, citrus fruit, citrous fruit
any of numerous fruits of the genus Citrus having thick rind and juicy pulp grown in warm regions
2. citrus, citrus tree
any of numerous tropical usually thorny evergreen trees of the genus Citrus having leathery evergreen leaves and widely cultivated for their juicy edible fruits having leathery aromatic rinds
Source: WordNet® (An amazing lexical database of English)
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