adj

• (anatomy, zootomy) Of or pertaining to the lips or labia.
  "The wound that does not kill Christ is the magical labial wound; it is the seal of the resurrection and an expression of the myth of eternal recurrence."
• (linguistics, phonetics) Articulated by the lips, as the consonants b, m and w.
• (dentistry, of an incisor or canine) On the side facing the lips. See mesial.
• (music) Furnished with lips.
  "a labial organ pipe"

noun

• (linguistics, phonetics) A consonant articulated by the lips.
  "The motions of the Tongue, Lips, Throat, Palate, & c. which go to the making of the ſeveral Alphabetical Letters are worthy inquiry, and pertinent to the preſent Inquiſition of Sounds: But becauſe they are ſubtil and long to deſcribe, we will refer them over, and place them amongſt the Experiments of Speech. The Hebrews have been diligent in it, and have aſſigned which Letters are Labial, which Dental, which Guttural, & c"
• (music) An organ pipe having a lip that influences its sound.
  "All organ pipes are divided into two general classes, labial and lingual pipes. The main difference between the two classes is the manner by which the vibrations producing the sound are caused. In labial pipes the column of air entering the pipe under pressure is set in vibration by a fixed obstruction at the mount of the pipe. […] [T]he obstruction at the mouth […] causes the column of air to vibrate. In the lingual or reed pipe, the vibrations are caused by the air passing through a metal reed, which causes the tongue of the reed to vibrate, thereby setting up sympathetic vibrations in the column of air in the pipe."
• (zootomy) Any of the scales bordering the mouth opening of a reptile.