The Collaborative International Dictionary of English v.0.48:

Venerable \Ven"er*a*ble\, a. [L. venerabilis: cf. F.
   v['e]n['e]rable.]
   1. Capable of being venerated; worthy of veneration or
      reverence; deserving of honor and respect; -- generally
      implying an advanced age; as, a venerable magistrate; a
      venerable parent.
      [1913 Webster]

            He was a man of eternal self-sacrifice, and that is
            always venerable.                     --De Quincey.
      [1913 Webster]

            Venerable men! you have come down to us from a
            former generation.                    --D. Webster.
      [1913 Webster]

   2. Rendered sacred by religious or other associations; that
      should be regarded with awe and treated with reverence;
      as, the venerable walls of a temple or a church.
      [1913 Webster]

   Note: This word is employed in the Church of England as a
         title for an archdeacon. In the Roman Catholic Church,
         venerable is applied to those who have attained to the
         lowest of the three recognized degrees of sanctity, but
         are not among the beatified, nor the canonized.
         [1913 Webster] -- Ven"er*a*ble*ness, n. --
         Ven"er*a*bly, adv.
         [1913 Webster]

WordNet (r) 3.0 (2006):

venerable
    adj 1: impressive by reason of age; "a venerable sage with white
           hair and beard"
    2: profoundly honored; "revered holy men" [syn: august,
       revered, venerable]

Moby Thesaurus II by Grady Ward, 1.0:

138 Moby Thesaurus words for "venerable":
   acknowledged, admirable, admitted, advanced, advanced in life,
   advanced in years, age-old, aged, ageless, along in years, ancient,
   antediluvian, antique, aristocratic, august, auld, awe-inspiring,
   awesome, awful, conventional, courtly, creditable, customary,
   dateless, dignified, divine, dreadful, elderly, established,
   esteemed, estimable, fixed, folk, grand, grave, gray,
   gray with age, gray-haired, gray-headed, grown old, hallowed,
   handed down, heavenly, held in esteem, heroic, highly esteemed,
   highly regarded, highly reputed, highly respectable, hoar, hoary,
   holy, honorable, honored, immemorial, imposing, impressive,
   in favor, in good odor, in high favor, ineffable, inenarrable,
   inexpressible, inveterate, inviolable, inviolate, kingly,
   legendary, long-established, long-standing, lordly, magisterial,
   majestic, meritorious, mythological, noble, numinous,
   of long standing, of old, of the folk, of yore, old,
   old as Methuselah, old as history, old as time, old-time, olden,
   oral, patriarchal, prescriptive, prestigious, princely, queenly,
   received, recognized, regal, religious, reputable, respectable,
   respected, revered, reverenced, reverend, reverential, rooted,
   royal, sacred, sacrosanct, sedate, senectuous, sober, solemn,
   spiritual, stately, statuesque, time-honored, timeless, timeworn,
   traditional, tried and true, true-blue, understood, unspeakable,
   untouchable, unutterable, unwritten, venerated, well-thought-of,
   white, white with age, white-bearded, white-crowned, white-haired,
   worshipful, worthy, wrinkled, wrinkly, years old