Source : Webster's Revised Unabridged Dictionary (1913)

Velum \Ve"lum\, n.; pl. {Vela}. [L., an awning, a veil. See
   {Veil}.]
   1. (Anat.) Curtain or covering; -- applied to various
      membranous partitions, especially to the soft palate. See
      under {Palate}.

   2. (Bot.)
      (a) See {Veil}, n., 3
      (b) .
      (b) A thin membrane surrounding the sporocarps of
          quillworts {Isoetes}).

   3. (Zo["o]l.) A veil-like organ or part. Especially:
      (a) The circular membrane that partially incloses the
          space beneath the umbrella of hydroid medus[ae].
      (b) A delicate funnel-like membrane around the flagellum
          of certain Infusoria. See Illust. a of {Protozoa}.

Source : WordNet®

velum
     n 1: membrane of the young sporophore of various mushrooms
          extending from the margin of the cap to the stem and is
          ruptured by growth; represented in mature mushroom by an
          annulus around the stem and sometimes a cortina on the
          margin of the cap [syn: {partial veil}]
     2: membrane initially completely investing the young sporophore
        of various mushrooms that is ruptured by growth;
        represented in the mature mushroom by a volva around lower
        part of stem and scales on upper surface of the cap [syn:
        {universal veil}]
     3: a muscular flap that closes off the nasopharynx during
        swallowing or speaking [syn: {soft palate}]
     [also: {vela} (pl)]