The Collaborative International Dictionary of English v.0.48:

High-pressure \High"-pres`sure\ (?; 135), a.
   1. Having or involving a pressure greatly exceeding that of
      the atmosphere; -- said of steam, air, water, etc., and of
      steam, air, or hydraulic engines, water wheels, etc.
      [1913 Webster]

   2. Fig.: Urgent; intense; as, a high-pressure business or
      social life.
      [1913 Webster]

   3. Using intense psychological pressure or other incentives
      to convince others to do things; aggressively persistent;
      as, high-pressure salesmen; high-pressure tactics.
      [PJC]

   High-pressure engine, an engine in which steam at high
      pressure is used. It may be either a condensing or a
      noncondensing engine. Formerly the term was used only of
      the latter. See Steam engine.
      [1913 Webster]

WordNet (r) 3.0 (2006):

high-pressure
    adj 1: aggressively and persistently persuasive; "a hard-hitting
           advertising campaign"; "a high-pressure salesman" [syn:
           hard-hitting, high-pressure]