anticlockwise

Anticlockwise, also called counterclockwise in American English, describes rotation or orientation in the opposite direction to the hands of a clock. On a clock face, anticlockwise motion proceeds from the 12 toward the 11, then 10, and so on.

Usage varies by region. Anticlockwise is standard in British English and many Commonwealth varieties, while counterclockwise is common in American English. In technical writing, both terms are widely understood; authors may specify the reference viewpoint to avoid ambiguity.

In mathematics and physics, anticlockwise is often treated as the positive sense of rotation. Angles measured from the positive x-axis increase anticlockwise; in the complex plane, a point traces the unit circle as θ grows in the anticlockwise direction. In three dimensions, the right-hand rule links anticlockwise rotation when viewed from the positive end of an axis to a positive rotation about that axis.

Etymology: the term derives from anti- meaning against and clockwise, the direction of a clock’s rotation. The concept is a convention and is defined relative to a chosen reference frame and viewpoint.