How many letters does the top answer for “to modify by contraction of the lip opening.” have?

The most common answer is labialize (9 letters).

Crossword clue: to modify by contraction of the lip opening.

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

labialize 9 letters web-def

pronounce with rounded lips