How many letters does the top answer for “a consonant whose articulation involves movement of the lips” have?

The most common answer is labial (6 letters).

Crossword clue: a consonant whose articulation involves movement of the lips

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

labial 6 letters wn-def

a consonant whose articulation involves movement of the lips