ADJECTIVE (3)

1. (of animals) tending to form a group with others of the same species;
- Example: "gregarious bird species"

2. instinctively or temperamentally seeking and enjoying the company of others;
- Example: "he is a gregarious person who avoids solitude"

3. (of plants) growing in groups that are close together;

The Collaborative International Dictionary of English v.0.48:

Gregarious \Gre*ga"ri*ous\, a. [L. gregarius, fr. grex, gregis,
   herd; cf. Gr. ? to assemble, Skr. jar to approach. Cf.
   Congregate, Egregious.]
   Habitually living or moving in flocks or herds; tending to
   flock or herd together; not habitually solitary or living
   alone. --Burke.
   [1913 Webster]

         No birds of prey are gregarious.         --Ray.

WordNet (r) 3.0 (2006):

gregarious
    adj 1: (of animals) tending to form a group with others of the
           same species; "gregarious bird species" [ant:
           ungregarious]
    2: instinctively or temperamentally seeking and enjoying the
       company of others; "he is a gregarious person who avoids
       solitude"
    3: (of plants) growing in groups that are close together [ant:
       ungregarious]