The Collaborative International Dictionary of English v.0.48:

Gloaming \Gloam"ing\, n. [See Gloom.]
   1. Twilight; dusk; the fall of the evening. [Scot. & North of
      Eng., and in poetry.] --Hogg.
      [1913 Webster]

   2. Sullenness; melancholy. [Obs.] --J. Still.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gloaming
    n 1: the time of day immediately following sunset; "he loved the
         twilight"; "they finished before the fall of night" [syn:
         twilight, dusk, gloaming, gloam, nightfall,
         evenfall, fall, crepuscule, crepuscle]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "gloaming":
   bad light, brown of dusk, brownness, candlelight, candlelighting,
   cocklight, crepuscule, darkishness, darksomeness, deadness, dim,
   dim light, dimness, dimpsy, drabness, dullness, dusk, duskiness,
   duskingtide, duskness, eventide, flatness, gloam, glooming,
   half-light, lack of sparkle, lackluster, lifelessness,
   lusterlessness, mat, mat finish, murk, murkiness, nightfall,
   owllight, partial darkness, semidark, somberness, twilight