That which prevents; -- incorrectly used instead of
preventive.
1. (Geom.) The eighth part of a circle; an arc of 45 degrees. 2. (Astron. & Astrol.) The position or aspect of a heavenly body, as the moon or a planet, when half way between conjunction, or opposition, and quadrature, or distant from another body 45 degrees. 3. An instrument for measuring a...