The Collaborative International Dictionary of English v.0.48:

Pressure \Pres"sure\ (?; 138), n. [OF., fr. L. pressura, fr.
   premere. See 4th Press.]
   1. The act of pressing, or the condition of being pressed;
      compression; a squeezing; a crushing; as, a pressure of
      the hand.
      [1913 Webster]

   2. A contrasting force or impulse of any kind; as, the
      pressure of poverty; the pressure of taxes; the pressure
      of motives on the mind; the pressure of civilization.
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            Where the pressure of danger was not felt.
                                                  --Macaulay.
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   3. Affliction; distress; grievance.
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            My people's pressures are grievous.   --Eikon
                                                  Basilike.
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            In the midst of his great troubles and pressures.
                                                  --Atterbury.
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   4. Urgency; as, the pressure of business.
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   5. Impression; stamp; character impressed.
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            All saws of books, all forms, all pressures past.
                                                  --Shak.
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   6. (Mech.) The action of a force against some obstacle or
      opposing force; a force in the nature of a thrust,
      distributed over a surface, often estimated with reference
      to the amount upon a unit's area.
      [1913 Webster]

   7. Electro-motive force.
      [Webster 1913 Suppl.]

   Atmospheric pressure, Center of pressure, etc. See under
      Atmospheric, Center, etc.

   Back pressure (Steam engine), pressure which resists the
      motion of the piston, as the pressure of exhaust steam
      which does not find free outlet.

   Fluid pressure, pressure like that exerted by a fluid. It
      is a thrust which is normal and equally intense in all
      directions around a point. --Rankine.

   Pressure gauge, a gauge for indicating fluid pressure; a
      manometer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pressure gauge
    n 1: gauge for measuring and indicating fluid pressure [syn:
         pressure gauge, pressure gage]