The Collaborative International Dictionary of English v.0.48:

Pharos \Pha"ros\, n. [L., fr. Gr. fa`ros, fr. Fa`ros an island
   in the Bay of Alexandria, where king Ptolemy Philadelphus
   built a famous lighthouse, one of the seven wonders of the
   ancient world.]
   A lighthouse or beacon for the guidance of seamen.
   [1913 Webster]

         He . . . built a pharos, or lighthouse.  --Arbuthnot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pharos
    n 1: a tower with a light that gives warning of shoals to
         passing ships [syn: beacon, lighthouse, beacon light,
         pharos]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "pharos":
   Texas tower, beacon, belvedere, bench mark, bleachers, bookmark,
   bridge, cairn, catstone, conning tower, gallery, gazebo,
   grandstand, landmark, lighthouse, lightship, lookout, loophole,
   mark, marker, menhir, milepost, milestone, monument,
   observation post, observatory, outlook, overlook, peanut gallery,
   peephole, platform, ringside, ringside seat, seamark, sighthole,
   top gallery, tower, watchtower



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PHAROS. A light-house or beacon. It is derived from Phams, a small island at
the mouth of the Nile, on which was built a watch-tower.