How many letters does the top answer for “a name derived from the name of your mother or a maternal ancestor” have?

The most common answer is matronymic (10 letters).

Crossword clue: a name derived from the name of your mother or a maternal ancestor

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

matronymic 10 letters wn-def

a name derived from the name of your mother or a maternal ancestor

metronymic 10 letters wn-def

a name derived from the name of your mother or a maternal ancestor