How many letters does the top answer for “the property of having two dimensions” have?

The most common answer is flatness (8 letters).

Crossword clue: the property of having two dimensions

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

flatness 8 letters wn-def

the property of having two dimensions

involving or having two dimensions 60% similar → planar

the property of having one dimension 60% similar → linearity

the spatial property of having dimensions 60% similar → dimensionality