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

Moby Thesaurus II by Grady Ward, 1.0:

188 Moby Thesaurus words for "transient":
   able to adapt, adaptable, adjustable, adventurer, alpinist,
   alterable, alterative, arising, astronaut, board-and-roomer,
   boarder, brief, brittle, camper, capricious, changeable, checkered,
   circumforaneous, climber, comers and goers, coming, commuter,
   compact, compendious, concise, corruptible, cosmopolite, cruiser,
   curt, curtal, curtate, deciduous, decurtate, disappearing,
   discursive, dissolving, divagatory, drifting, dying, emanating,
   emanative, emanent, emergent, emerging, ephemeral, errant,
   evanescent, evaporating, ever-changing, excursionist, explorer,
   fading, fare, fickle, fleeting, flexible, flitting, floating,
   fluid, fly-by-night, flying, footloose, footloose and fancy-free,
   forthcoming, fragile, frail, fugacious, fugitive, gadding,
   globe-girdler, globe-trotter, goer, gypsy-like, gypsyish, hajji,
   impermanent, impetuous, impulsive, inconstant, instantaneous,
   insubstantial, issuing, jet set, jet-setter, journeyer,
   kaleidoscopic, landloping, lessee, little, lodger, low, malleable,
   many-sided, mariner, meandering, melting, metamorphic, migrational,
   migratory, mobile, modifiable, momentaneous, momentary, mortal,
   mountaineer, movable, mutable, nomad, nomadic, nondurable,
   nonpermanent, nonuniform, palmer, passenger, passer, passerby,
   passing, pathfinder, paying guest, perishable, permutable, pilgrim,
   pioneer, plastic, protean, proteiform, rambling, ranging, renter,
   resilient, roaming, roomer, roving, rubberneck, rubbernecker,
   rubbery, sailor, shifting, short, short and sweet, short-lived,
   short-term, sightseer, sojourner, straggling, straphanger,
   straying, strolling, subject to death, succinct, summary, supple,
   surfacing, synoptic, temporal, temporary, temporary lodger, tenant,
   tourer, tourist, trailblazer, trailbreaker, traipsing, transeunt,
   transient guest, transitive, transitory, transmigratory, traveler,
   trekker, tripper, underlessee, undurable, unenduring, unstable,
   vagabond, vagrant, vanishing, variable, viator, visiting fireman,
   volatile, voortrekker, voyager, voyageur, wandering, wayfarer,
   world-traveler



The Free On-line Dictionary of Computing (30 December 2018):

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)