How many letters does the top answer for “a word having more than one form of the root.” have?

The most common answer is metaplast (9 letters).

Crossword clue: a word having more than one form of the root.

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

metaplast 9 letters web-def

A word having more than one form of the root.

having more than one nucleolus. 50% similar → polynucleolar

having more than one story 50% similar → multistoried, multistory

having one or more sepals. 50% similar → sepaled