The Collaborative International Dictionary of English v.0.48:

Labial \La"bi*al\, a. [LL. labialis, fr. L. labium lip: cf. F.
   labial. See Lip.]
   1. Of or pertaining to the lips or labia; as, labial veins.
      [1913 Webster]

   2. (Mus.) Furnished with lips; as, a labial organ pipe.
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   3. (Phonetics)
      (a) Articulated, as a consonant, mainly by the lips, as b,
          p, m, w.
      (b) Modified, as a vowel, by contraction of the lip
          opening, as [=oo] (f[=oo]d), [=o] ([=o]ld), etc., and
          as eu and u in French, and ["o], ["u] in German. See
          Guide to Pronunciation, [sect][sect] 11, 178.
          [1913 Webster]

   4. (Zool.) Of or pertaining to the labium; as, the labial
      palpi of insects. See Labium.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Labial \La"bi*al\, n.
   1. (Phonetics) A letter or character representing an
      articulation or sound formed or uttered chiefly with the
      lips, as b, p, w.
      [1913 Webster]

   2. (Mus.) An organ pipe that is furnished with lips; a flue
      pipe.
      [1913 Webster]

   3. (Zool.) One of the scales which border the mouth of a fish
      or reptile.
      [1913 Webster]

WordNet (r) 3.0 (2006):

labial
    adj 1: of or relating to the lips of the mouth; "labial stops"
    2: relating to or near the female labium
    n 1: a consonant whose articulation involves movement of the
         lips [syn: labial consonant, labial]