The Collaborative International Dictionary of English v.0.48:

Impend \Im*pend"\, v. i. [imp. & p. p. Impended; p. pr. & vb.
   n. Impending.] [L. impend[=e]re; pref. im- in + pend[=e]re
   to hang. See Pendant.]
   To hang over; to be suspended above; to threaten from near at
   hand; to menace; to be imminent. See Imminent.
   [1913 Webster]

         Destruction sure o'er all your heads impends. --Pope.
   Impendence

The Collaborative International Dictionary of English v.0.48:

Impending \Im*pend"ing\, a.
   Hanging over; overhanging; suspended so as to menace;
   imminet; threatening.
   [1913 Webster]

         An impending brow.                       --Hawthorne.
   [1913 Webster]

         And nodding Ilion waits th' impending fall. --Pope.

   Syn: Imminent; threatening. See Imminent.
        [1913 Webster]

WordNet (r) 3.0 (2006):

impending
    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:

50 Moby Thesaurus words for "impending":
   about to be, already in sight, approaching, at hand, beetle,
   beetle-browed, beetling, brewing, close, close at hand, coming,
   forthcoming, future, gathering, going to happen, immediate,
   imminent, impendent, in danger imminent, in prospect, in reserve,
   in store, in the air, in the cards, in the offing, in the wind,
   in view, incumbent, instant, jutting, looming, lowering, lurking,
   menacing, near, near at hand, nearing, on the horizon, overhanging,
   overhung, pending, preparing, projecting, proximate,
   superincumbent, that will be, threatening, to come, upcoming,
   waiting