The Collaborative International Dictionary of English v.0.48:

Imminent \Im"mi*nent\, a. [L. imminens, p. pr. of imminere to
   project; pref. im- in + minere (in comp.) to jut, project.
   See Eminent.]
   1. Threatening to occur immediately; near at hand; impending;
      -- said especially of misfortune or peril. "In danger
      imminent." --Spenser.
      [1913 Webster]

   2. Full of danger; threatening; menacing; perilous.
      [1913 Webster]

            Hairbreadth scapes i' the imminent deadly breach.
                                                  --Shak.
      [1913 Webster]

   3. (With upon) Bent upon; attentive to. [R.]
      [1913 Webster]

            Their eyes ever imminent upon worldly matters.
                                                  --Milton.

   Syn: Impending; threatening; near; at hand.

   Usage: Imminent, Impending, Threatening. Imminent is
          the strongest: it denotes that something is ready to
          fall or happen on the instant; as, in imminent danger
          of one's life. Impending denotes that something hangs
          suspended over us, and may so remain indefinitely; as,
          the impending evils of war. Threatening supposes some
          danger in prospect, but more remote; as, threatening
          indications for the future.
          [1913 Webster]

                Three times to-day
                You have defended me from imminent death.
                                                  --Shak.
          [1913 Webster]

                No story I unfold of public woes,
                Nor bear advices of impending foes. --Pope.
          [1913 Webster]

                Fierce faces threatening war.     --Milton.
          [1913 Webster]

WordNet (r) 3.0 (2006):

imminent
    adj 1: close in time; about to occur; "retribution is at hand";
           "some people believe the day of judgment is close at
           hand"; "in imminent danger"; "his impending retirement"
           [syn: at hand(p), close at hand(p), imminent,
           impendent, impending]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "imminent":
   about to be, abusive, advancing, alarming, already in sight,
   anticipated, approaching, approximate, approximative, at hand,
   attracted to, awaited, bludgeoning, blustering, brewing,
   browbeating, bulldozing, bullying, close, close at hand, coming,
   comminatory, denunciatory, desired, destinal, destined, determined,
   drawn to, due, emergent, eventual, expected, extrapolated, fatal,
   fated, fatidic, fear-inspiring, foreboding, foreseen, forthcoming,
   future, futuristic, gathering, going to happen, hectoring,
   hereafter, hoped-for, immediate, impendent, impending,
   in danger imminent, in prospect, in reserve, in store,
   in the cards, in the offing, in the wind, in view, ineluctable,
   inescapable, inevasible, inevitable, instant, intimidating, later,
   likely, long-expected, looming, lowering, lurking, menacing,
   minacious, minatory, momentary, near, near at hand, nearing, nigh,
   ominous, on the horizon, oncoming, overdue, overhanging, pending,
   planned, plotted, possible, predicted, preparing, presumed,
   probable, projected, promised, prophesied, prospective, proximate,
   sinister, terroristic, terrorizing, that will be, threatening,
   threatful, to come, to-be, ultimate, unavoidable, upcoming,
   waiting