The Collaborative International Dictionary of English v.0.48:

critical point \crit"ic*al point\ (Physics),
   That combination of volume and pressure, at the critical
   temperature of the substance, at which the liquid and gaseous
   phases of a given quantity of a substance have identical
   values for their densities and other properties.
   [PJC]

WordNet (r) 3.0 (2006):

critical point
    n 1: a crisis situation or point in time when a critical
         decision must be made; "at that juncture he had no idea
         what to do"; "he must be made to realize that the company
         stands at a critical point" [syn: juncture, critical
         point, crossroads]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "critical point":
   bench mark, cardinal point, chief thing, climacteric, climax,
   clutch, convergence of events, core, cornerstone, crisis,
   critical juncture, crossroads, crucial period, crunch, crux,
   emergency, essence, essential, essential matter, exigency,
   extremity, fundamental, gist, gravamen, great point, heart,
   high point, hinge, important thing, issue, kernel, keystone,
   landmark, main point, main thing, material point, meat, milestone,
   nub, pass, pinch, pith, pivot, push, real issue, rub,
   salient point, sine qua non, strait, substance, substantive point,
   the bottom line, the point, turn, turning point