The Collaborative International Dictionary of English v.0.48:

Penetrate \Pen"e*trate\, v. i.
   To pass; to make way; to pierce. Also used figuratively.
   [1913 Webster]

         Preparing to penetrate to the north and west. --J. R.
                                                  Green.
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         Born where Heaven's influence scarce can penetrate.
                                                  --Pope.
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         The sweet of life that penetrates so near. --Daniel.
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The Collaborative International Dictionary of English v.0.48:

Penetrate \Pen"e*trate\, v. t. [imp. & p. p. Penetrated; p.
   pr. & vb. n. Penetrating.] [L. penetratus, p. p. of
   penetrare to penetrate; akin to penitus inward, inwardly, and
   perh. to pens with, in the power of, penus store of food,
   innermost part of a temple.]
   1. To enter into; to make way into the interior of; to effect
      an entrance into; to pierce; as, light penetrates
      darkness.
      [1913 Webster]

   2. To affect profoundly through the senses or feelings; to
      touch with feeling; to make sensible; to move deeply; as,
      to penetrate one's heart with pity. --Shak.
      [1913 Webster]

            The translator of Homer should penetrate himself
            with a sense of the plainness and directness of
            Homer's style.                        --M. Arnold.
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   3. To pierce into by the mind; to arrive at the inner
      contents or meaning of, as of a mysterious or difficult
      subject; to comprehend; to understand.
      [1913 Webster]

            Things which here were too subtile for us to
            penetrate.                            --Ray.
      [1913 Webster]

WordNet (r) 3.0 (2006):

penetrate
    v 1: pass into or through, often by overcoming resistance; "The
         bullet penetrated her chest" [syn: penetrate,
         perforate]
    2: come to understand [syn: penetrate, fathom, bottom]
    3: become clear or enter one's consciousness or emotions; "It
       dawned on him that she had betrayed him"; "she was penetrated
       with sorrow" [syn: click, get through, dawn, come
       home, get across, sink in, penetrate, fall into
       place]
    4: enter a group or organization in order to spy on the members;
       "The student organization was infiltrated by a traitor" [syn:
       infiltrate, penetrate]
    5: make one's way deeper into or through; "The hikers did not
       manage to penetrate the dense forest"
    6: insert the penis into the vagina or anus of; "Did the
       molester penetrate the child?"
    7: spread or diffuse through; "An atmosphere of distrust has
       permeated this administration"; "music penetrated the entire
       building"; "His campaign was riddled with accusations and
       personal attacks" [syn: permeate, pervade, penetrate,
       interpenetrate, diffuse, imbue, riddle]

Moby Thesaurus II by Grady Ward, 1.0:

189 Moby Thesaurus words for "penetrate":
   affect, auger, be glimpsed, be hep to, be on to, be realized,
   be remembered, be wise to, benumb, bespread, besprinkle, bite,
   bore, breathe, brew, broach, catch on to, charge, chill, color,
   come across, come alive, come home to, come in, come through,
   comprehend, countersink, crawl with, creep with, cut, dawn on,
   decoct, descry, diffuse, dig, discern, discover, dredge, drill,
   drive, dye, ease in, empierce, encroach, enter, entincture,
   extend throughout, fathom, figure out, fill, find out, fix, flavor,
   freeze, frost, frostbite, gain entree, get, get across, get at,
   get into, get over, get through, get to, go deep, go in, go into,
   go through, go through one, gore, gouge, gouge out, grasp, hit,
   hole, honeycomb, imbrue, imbue, impale, impregnate, infiltrate,
   infuse, ingress, inject, inoculate, insert, insinuate, instill,
   interject, interpenetrate, interpolate, introduce, intromit,
   invade, jab, knife, lance, leave no void, leaven, make an entrance,
   make an impression, make out, make way into, melt, melt the heart,
   move, needle, never be forgotten, nip, numb, obsess, occupy,
   overrun, overspread, overswarm, pass through, perceive, percolate,
   perforate, perfuse, permeate, pervade, pierce, pink, plumb, pop in,
   prick, probe, punch, puncture, put in, rankle, reach, ream,
   ream out, refrigerate, register, riddle, run through, saturate,
   season, see, see daylight, see into, see the light, see through,
   seep in, sense, set in, sink in, skewer, slip in, smart, soak in,
   soften, spear, spike, spit, stab, steep, stick, stick in, sting,
   stir, strike, suffuse, swarm with, tap, teem with, temper,
   throw in, tincture, tinge, touch, touch a chord, transfix,
   transfuse, transpierce, trepan, trephine, trespass, tuck in,
   tumble to, uncover, understand, unravel, whip in, wise up to,
   work out