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]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "gregarious":
   affable, all jaw, amiable, candid, chatty, civil, clubbable,
   clubbish, clubby, communicative, companionable, companionate,
   compatible, congenial, conversational, courteous, effusive,
   expansive, fit for society, flip, fluent, fond of society, frank,
   friendly, gabby, garrulous, gassy, genial, glib, gossipy, gushy,
   hospitable, long-winded, loquacious, multiloquent, multiloquious,
   newsy, overtalkative, prolix, smooth, sociable, social,
   social-minded, talkative, talky, urbane, verbose, voluble, windy