The Collaborative International Dictionary of English v.0.48:

Pinnacle \Pin"na*cle\, n. [OE. pinacle, F. pinacle, L.
   pinnaculum, fr. pinna pinnacle, feather. See Pin a peg.]
   1. (Arch.) An architectural member, upright, and generally
      ending in a small spire, -- used to finish a buttress, to
      constitute a part in a proportion, as where pinnacles
      flank a gable or spire, and the like. Pinnacles may be
      considered primarily as added weight, where it is
      necessary to resist the thrust of an arch, etc.
      [1913 Webster]

            Some renowned metropolis
            With glistering spires and pinnacles around.
                                                  --Milton.
      [1913 Webster]

   2. Anything resembling a pinnacle; a lofty peak; a pointed
      summit.
      [1913 Webster]

            Three silent pinnacles of aged snow.  --Tennyson.
      [1913 Webster]

            The slippery tops of human state,
            The gilded pinnacles of fate.         --Cowley.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pinnacle \Pin"na*cle\, v. t. [imp. & p. p. Pinnacled; p. pr. &
   vb. n. Pinnacling.]
   To build or furnish with a pinnacle or pinnacles. --T.
   Warton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pinnacle
    n 1: (architecture) a slender upright spire at the top of a
         buttress of tower
    2: the highest level or degree attainable; the highest stage of
       development; "his landscapes were deemed the acme of beauty";
       "the artist's gifts are at their acme"; "at the height of her
       career"; "the peak of perfection"; "summer was at its peak";
       "...catapulted Einstein to the pinnacle of fame"; "the summit
       of his ambition"; "so many highest superlatives achieved by
       man"; "at the top of his profession" [syn: acme, height,
       elevation, peak, pinnacle, summit, superlative,
       meridian, tiptop, top]
    3: a lofty peak
    v 1: surmount with a pinnacle; "pinnacle a pediment"
    2: raise on or as if on a pinnacle; "He did not want to be
       pinnacled"

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "pinnacle":
   acme, acme of perfection, all, antenna tower, apex, apogee,
   barbican, belfry, bell tower, brow, campanile, cap, ceiling,
   climax, cloud nine, colossus, column, consummation, crest, crown,
   culmen, culmination, cupola, derrick, dome, edge, end, extreme,
   extreme limit, extremity, fire tower, heaven, heavens, height,
   high noon, highest degree, highest pitch, highest point, hilltop,
   knoll, lantern, last word, lighthouse, limit, lofty peak, martello,
   martello tower, mast, maximum, meridian, minaret, monument,
   mountaintop, ne plus ultra, no place higher, noon, nth degree,
   obelisk, observation tower, pagoda, peak, perfection, pic, pico,
   pike, pilaster, pillar, pink, pink of perfection, pitch, point,
   pole, precipice, pylon, pyramid, ridge, seventh heaven, shaft, sky,
   skyscraper, spire, spur, standpipe, steeple, stupa, summit,
   television mast, the whole, tip, tip-top, top, tope, tor, tour,
   tower, turret, ultimate, upmost, upper extremity, uppermost,
   utmost, utmost extent, uttermost, vertex, very top, water tower,
   windmill tower, zenith



Easton's 1897 Bible Dictionary:

Pinnacle
   a little wing, (Matt. 4:5; Luke 4:9). On the southern side of
   the temple court was a range of porches or cloisters forming
   three arcades. At the south-eastern corner the roof of this
   cloister was some 300 feet above the Kidron valley. The
   pinnacle, some parapet or wing-like projection, was above this
   roof, and hence at a great height, probably 350 feet or more
   above the valley.