means A four-sided shape with four right angles, where opposite sides are equal in length.

from From Latin 'rectus' (right, straight) plus 'angulus' (angle, corner) — literally a 'right-angled' figure. The 'rectus' root is a sprawling family: it also gives us 'correct,' 'direct,' 'erect,' and 'rectify,' all sharing that ancestral sense of straightness and setting-things-right. 'Angulus,' the corner, is possibly a cousin of 'ankle' — both bend at a joint. The English word arrived in the late 16th century, assembled tidily from these Latin parts to name the shape that keeps everything square.