How many letters does the top answer for “not reflecting light; not glossy” have?

The most common answer is mat (3 letters).

Crossword clue: not reflecting light; not glossy

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

mat 3 letters wn-def

a thick flat pad used as a floor covering

matt 4 letters wn-def

the property of having little or no contrast; lacking highlights or gloss

matte 5 letters wn-def

the property of having little or no contrast; lacking highlights or gloss