How many letters does the top answer for “the line or plane indicating the limit or extent of something” have?

The most common answer is boundary (8 letters).

Crossword clue: the line or plane indicating the limit or extent of something

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

boundary 8 letters wn-def

the line or plane indicating the limit or extent of something

bounds 6 letters wn-def

the line or plane indicating the limit or extent of something