How many letters does the top answer for “the roughness of a substance that causes abrasions” have?

The most common answer is harshness (9 letters).

Crossword clue: the roughness of a substance that causes abrasions

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

harshness 9 letters wn-def

the roughness of a substance that causes abrasions

scratchiness 12 letters wn-def

the roughness of a substance that causes abrasions