The Collaborative International Dictionary of English v.0.48:

Penetrating \Pen"e*tra`ting\, a.
   1. Having the power of entering, piercing, or pervading;
      sharp; subtile; penetrative; as, a penetrating odor.
      [1913 Webster]

   2. Acute; discerning; sagacious; quick to discover; as, a
      penetrating mind.
      [1913 Webster]

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.
      [1913 Webster]

   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):

penetrating
    adj 1: having or demonstrating ability to recognize or draw fine
           distinctions; "an acute observer of politics and
           politicians"; "incisive comments"; "icy knifelike
           reasoning"; "as sharp and incisive as the stroke of a
           fang"; "penetrating insight"; "frequent penetrative
           observations" [syn: acute, discriminating,
           incisive, keen, knifelike, penetrating,
           penetrative, piercing, sharp]
    2: tending to penetrate; having the power of entering or
       piercing; "a toxic penetrative spray applied to the surface";
       "a cold penetrating wind"; "a penetrating odor" [syn:
       penetrative, penetrating]

Moby Thesaurus II by Grady Ward, 1.0:

185 Moby Thesaurus words for "penetrating":
   Siberian, absorbing, acerb, acerbate, acerbic, acid, acidic,
   acidulent, acidulous, acrid, acrimonious, acute, algid,
   apperceptive, appercipient, arctic, argute, asperous, astringent,
   astute, below zero, biting, bitter, bitterly cold, bleak, boreal,
   brisk, brumal, caustic, clear-cut, clever, cogent, cold,
   cold as charity, cold as death, cold as ice, cold as marble,
   corroding, corrosive, creaky, crisp, cutting, deafening, deep,
   deep-felt, deepgoing, discerning, discriminating, double-edged,
   driving, ear-piercing, ear-splitting, edged, effective, escharotic,
   farseeing, farsighted, fierce, forceful, forcible, foreseeing,
   foresighted, forethoughted, forethoughtful, freezing,
   freezing cold, frigid, gelid, glacial, gutsy, harsh, heartfelt,
   hibernal, hiemal, homefelt, howling, hyperborean, ice-cold,
   ice-encrusted, icelike, icy, imperative, impressive, incisive,
   inclement, indelible, ingoing, intelligent, intense, irritating,
   keen, keening, longheaded, longsighted, loud, mordacious, mordant,
   nervous, nipping, nippy, nose-piercing, nose-tickling, numbing,
   perceptive, percipient, perspicacious, perspicuous, pervading,
   pervasive, piercing, pinching, piping, piquant, poignant, powerful,
   profound, provident, punchy, pungent, quick, quick-witted, raw,
   reedy, reeking, rigorous, rough, sagacious, scathing, scorching,
   screaky, screeching, screechy, searching, sensational, sensitive,
   severe, sharp, sharp-sighted, sharp-witted, shrieking, shrieky,
   shrill, sinewed, sinewy, slashing, sleety, slushy, smart, snappy,
   sour, squeaking, squeaky, stabbing, stinging, stone-cold, strident,
   striking, stringent, strong, strong-scented, strong-smelling,
   subzero, suffocating, supercooled, tart, telling, thin, thundering,
   trenchant, ululant, understanding, vehement, vigorous, violent,
   virulent, vital, vitriolic, wailing, whining, whistling,
   winterbound, winterlike, wintery, wintry, withering