How many letters does the top answer for “to make a testament, or will.” have?

The most common answer is test (4 letters).

Crossword clue: to make a testament, or will.

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

test 4 letters web-def

put to the test, as for its quality, or give experimental use to

a person who makes a will 50% similar → testate, testator

to make a will. fuller. 50% similar → testamentize