The Collaborative International Dictionary of English v.0.48:

Transient \Tran"sient\, a. [L. transiens, -entis, p. pr. of
   transire, transitum, to go or pass over. See Trance.]
   1. Passing before the sight or perception, or, as it were,
      moving over or across a space or scene viewed, and then
      disappearing; hence, of short duration; not permanent; not
      lasting or durable; not stationary; passing; fleeting;
      brief; transitory; as, transient pleasure. "Measured this
      transient world." --Milton.
      [1913 Webster]

   2. Hasty; momentary; imperfect; brief; as, a transient view
      of a landscape.
      [1913 Webster]

   3. Staying for a short time; not regular or permanent; as, a
      transient guest; transient boarders. [Colloq. U. S.]
      [1913 Webster]

   Syn: Transient, Transitory, Fleeting.

   Usage: Transient represents a thing as brief at the best;
          transitory, as liable at any moment to pass away.
          Fleeting goes further, and represents it as in the act
          of taking its flight. Life is transient; its joys are
          transitory; its hours are fleeting.
          [1913 Webster]

                What is loose love? A transient gust. --Pope
          [1913 Webster]

                If [we love] transitory things, which soon
                decay,
                Age must be loveliest at the latest day.
                                                  --Donne.
          [1913 Webster]

                O fleeting joys
                Of Paradise, dear bought with lasting woes.
                                                  --Milton.
          [1913 Webster] -- Tran"sient*ly, adv. --
          Tran"sient*ness, n.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Transient \Tran"sient\, n.
   That which remains but for a brief time. --Glanvill.
   [1913 Webster] Transilience

WordNet (r) 3.0 (2006):

transient
    adj 1: of a mental act; causing effects outside the mind [syn:
           transeunt, transient] [ant: immanent, subjective]
    2: lasting a very short time; "the ephemeral joys of childhood";
       "a passing fancy"; "youth's transient beauty"; "love is
       transitory but it is eternal"; "fugacious blossoms" [syn:
       ephemeral, passing, short-lived, transient,
       transitory, fugacious]
    n 1: one who stays for only a short time; "transient laborers"
    2: (physics) a short-lived oscillation in a system caused by a
       sudden change of voltage or current or load

The Free On-line Dictionary of Computing (19 January 2023):

transient

   1.  A sudden, brief increase in current or
   voltage in a circuit that can damage sensitive components
   and instruments.

   (2003-06-12)

   2.  A software object with a short and limited
   lifetime which is not saved for later reuse.

   (1998-04-19)