How many letters does the top answer for “the sister of your father or mother; the wife of your uncle” have?

The most common answer is aunt (4 letters).

Crossword clue: the sister of your father or mother; the wife of your uncle

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

aunt 4 letters wn-def

the sister of your father or mother; the wife of your uncle

auntie 6 letters wn-def

the sister of your father or mother; the wife of your uncle

aunty 5 letters wn-def

the sister of your father or mother; the wife of your uncle

an uncle of your father or mother 67% similar → granduncle

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

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