How many letters does the top answer for “a natural father or mother” have?

The most common answer is genitor (7 letters).

Crossword clue: a natural father or mother

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

genitor 7 letters wn-def

a natural father or mother

the father of your father or mother 50% similar → gramps, grandad, granddad

the mother of one's father or mother. 50% similar → grandmother

the mother of your father or mother 50% similar → gran, grandma, grandmother