Source : Webster's Revised Unabridged Dictionary (1913)

Fugacity \Fu*gac"i*ty\, a. [L fugacitas: cf. F. fugacit['e].]
   1. The quality of being fugacious; fugaclousness; volatility;
      as, fugacity of spirits. --Boyle.

   2. Uncertainty; instability. --Johnson.

Source : WordNet®

fugacity
     n 1: the tendency of a gas to expand or escape
     2: the lack of enduring qualities (used chiefly of plant parts)
        [syn: {fugaciousness}]