The Collaborative International Dictionary of English v.0.48:

Populous \Pop"u*lous\, a. [L. populosus, fr. populus people: cf.
   F. populeux.]
   1. Abounding in people; full of inhabitants; containing many
      inhabitants in proportion to the extent of the country.
      [1913 Webster]

            Heaven, yet populous, retains
            Number sufficient to possess her realms. --Milton.
      [1913 Webster]

   2. Popular; famous. [Obs.] --J. Webster.
      [1913 Webster]

   3. Common; vulgar. [Obs.] --Arden of Feversham.
      [1913 Webster]

   4. Numerous; in large number. [Obs.] "The dust . . . raised
      by your populous troops." --Shak.
      [1913 Webster] -- Pop"u*lous*ly, adv. --
      Pop"u*lous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

populous
    adj 1: densely populated [syn: populous, thickly settled]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "populous":
   alive with, bristling, bursting, close, colonized, compact,
   crammed, crawling, crowded, crowding, dense, empeopled, firm, full,
   in profusion, inhabited, jam-packed, jammed, lavish, legion,
   multifarious, multitudinal, multitudinous, numerous, occupied,
   overflowing, packed, peopled, populated, prodigal, profuse,
   proliferating, prolific, rife, serried, settled, several, solid,
   studded, sundry, superabundant, swarming, teeming, tenanted, thick,
   thick as hail, thick with, thick-coming, thronged, thronging,
   various, voluminous