How many letters does the top answer for “allowing light to pass through diffusely” have?

The most common answer is semitransparent (15 letters).

Crossword clue: allowing light to pass through diffusely

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

semitransparent 15 letters wn-def

allowing light to pass through diffusely

translucent 11 letters wn-def

allowing light to pass through diffusely

the quality of allowing light to pass diffusely 67% similar → translucence, translucency