How many letters does the top answer for “containing three hydroxyl groups” have?

The most common answer is trihydroxy (10 letters).

Crossword clue: containing three hydroxyl groups

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

trihydroxy 10 letters wn-def

containing three hydroxyl groups

being or containing a hydroxyl group 60% similar → hydroxy

an amide containing three amido groups. 50% similar → triamide

an amine containing three amido groups. 50% similar → triamine