1590s, "having an angle or angles, pointy," from Latin angularis "having corners or angles," from angulus "angle, corner" (see angle (n.)). Earlier in an astrological sense, "occupying a cardinal point of the zodiac" (late 14c.). Angulous "having many corners" is from mid-15c. Angular as "measured by an angle" is from 1670s, hence angular motion "motion of a body which moves around a fixed point."
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Harper, D. (n.d.). Etymology of equiangular. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/equiangular