| Definition -
A sound made with both lips, e.g. the [m] in mother and the [p] in popcorn.
1. When just one lip is used, the sound is called a labial, e.g. the [f] in filter.
Etymology - The word derives from the Latin bilabialis, two lipped (from labium, lip).
Oxford English Dictionary - Its first citation is from 1894:
"At some time before the fifth cent. a.d. … initial v … seems to have passed from the bilabial spirant (Spanish b) to the labio-dental spirant (our v)."
(W. M. Lindsay Lat. Lang. 47 )