Crossword clue: (geometry) a plane rectangle with four equal sides and four right angles; a four-sided regular polygon

The most common answer is foursquare (10 letters).

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

Possible answers

foursquare 10 letters wn-def

(geometry) a plane rectangle with four equal sides and four right angles; a four-sided regular polygon

square 6 letters wn-def

(geometry) a plane rectangle with four equal sides and four right angles; a four-sided regular polygon