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 )

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