The Collaborative International Dictionary of English v.0.48:

Precipitant \Pre*cip"i*tant\, n. (Chem.)
   Any force or reagent which causes the formation of a
   precipitate.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Precipitant \Pre*cip"i*tant\, a. [L. praecipitans, -antis, p.
   pr. of praecipitare: cf. F. pr['e]cipitant. See
   Precipitate.]
   1. Falling or rushing headlong; rushing swiftly, violently,
      or recklessly; moving precipitately.
      [1913 Webster]

            They leave their little lives
            Above the clouds, precipitant to earth. --J.
                                                  Philips.
      [1913 Webster]

            Should he return, that troop so blithe and bold,
            Precipitant in fear would wing their flight. --Pope.
      [1913 Webster]

   2. Unexpectedly or foolishly brought on or hastened; rashly
      hurried; hasty; sudden; reckless. --Jer. Taylor.
      "Precipitant rebellion." --Eikon Basilike.
      [1913 Webster]

WordNet (r) 3.0 (2006):

precipitant
    adj 1: done with very great haste and without due deliberation;
           "hasty marriage seldom proveth well"- Shakespeare; "hasty
           makeshifts take the place of planning"- Arthur Geddes;
           "rejected what was regarded as an overhasty plan for
           reconversion"; "wondered whether they had been rather
           precipitate in deposing the king" [syn: hasty,
           overhasty, precipitate, precipitant, precipitous]
    n 1: an agent that causes a precipitate to form