The Collaborative International Dictionary of English v.0.48:

oncoming \oncoming\ adj.
   moving toward one; approaching.

   Syn: approaching.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

oncoming \oncoming\ n.
   the beginning or early stages; the onset.

   Syn: onset.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

oncoming
    adj 1: moving toward one
    n 1: the beginning or early stages; "the onset of pneumonia"
         [syn: onset, oncoming]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "oncoming":
   A, access, accession, advance, advancing, advent, afflux,
   affluxion, alpha, approach, approaching, appropinquation,
   approximate, approximation, approximative, appulse, arrival,
   arriving, attracted to, beginning, blast-off, coming, coming near,
   coming toward, commencement, creation, cutting edge, dawn,
   drawn to, edge, establishment, flowing toward, flying start,
   forthcoming, forward, forward-looking, foundation, fresh start,
   go-ahead, imminence, imminent, institution, jump-off, kick-off,
   leading edge, moving, near, nearing, nearness, new departure,
   ongoing, onset, onward, opening, origin, origination, outbreak,
   outset, proceeding, progressing, progressive, proximate,
   proximation, running start, send-off, setting in motion,
   setting-up, square one, start, start-off, starting point, take-off,
   to come, upcoming