四角(しかく)

四角(しかく) is a general term for any four-sided shape — squares, rectangles, and other quadrilaterals. It is the everyday word; for precise geometric terms, see below.

FORMS:

• 四角(しかく) (noun): a square/rectangle
• 四角(しかく)い (i-adjective): square-shaped, boxy — the most natural adjectival form
• 四角(しかく)な (na-adjective): less common in everyday speech

PRECISE GEOMETRIC TERMS:

• 正方形(せいほうけい): square (all sides equal)
• 長方形(ちょうほうけい): rectangle
• 四角形(しかくけい): quadrilateral (formal/mathematical)

RELATED SHAPES:

• 三角(さんかく): triangle
• 丸(まる): circle
• 丸(まる)い: round (i-adjective)

USAGE:
In everyday conversation, 四角(しかく)い is used broadly to describe anything boxy or rectangular: 四角(しかく)い箱(はこ) (square box), 四角(しかく)い顔(かお) (square face).