How many letters does the top answer for “any of a class of alcohols having 2 hydroxyl groups in each molecule” have?

The most common answer is diol (4 letters).

Crossword clue: any of a class of alcohols having 2 hydroxyl groups in each molecule

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

diol 4 letters wn-def

any of a class of alcohols having 2 hydroxyl groups in each molecule

glycol 6 letters wn-def

any of a class of alcohols having 2 hydroxyl groups in each molecule