1A shape with four corners — a square or quadrilateral; used as a noun (or na-adjective) for boxy, angular shapes and objects. Often appears as the adjective 四角い.
このテーブルは四角だから、四人座れる。
This table is square, so four people can sit at it.
箱を四角に組み立てるのは意外と難しい。
Assembling a box into a proper square shape is surprisingly tricky.
彼の顔は四角で、意志が強そうに見える。
His face is square, giving him a strong-willed look.
折り紙を四角に切ってから鶴を折り始めた。
I cut the origami paper into a square before starting to fold a crane.