Wordnet 3.0
ADJECTIVE (2)
1. 
 of or relating to plants of the genus Citrus; 
- Example: "a citrous disease"2. 
 of or relating to or producing fruit of the plants of the genus Citrus; 
- Example: "the citrus production of Florida"
The Collaborative International Dictionary of English v.0.48:
citrous \citrous\ (s[i^]t"r[u^]s), adj.
   of or pertaining to a citrus tree; as, a citrous disease.
   Syn: citrus.
        [WordNet 1.5]
   2. of or pertaining to citrus. the citrus production of
      Florida
   Syn: citrus.
        [WordNet 1.5]
WordNet (r) 3.0 (2006):
citrous
    adj 1: of or relating to plants of the genus Citrus; "a citrous
           disease"
    2: of or relating to or producing fruit of the plants of the
       genus Citrus; "the citrus production of Florida"