How many letters does the top answer for “which painting was not made by vincent van gogh” have?

The most common answer is ninth (5 letters).

Crossword clue: which painting was not made by vincent van gogh

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

ninth 5 letters otdb

position nine in a countable series of things

wave 4 letters otdb

one of a series of ridges that moves across the surface of a liquid (especially across a large body of water)