The meaning of Erastus is Lovely and  Beloved. Its origin is Variant of the Greek name Erastos. Erastus is a form of Erastos and is generally pronounced like eh RAS tus. This name is mostly being used as a boys name. Last year it ranked 4,160th in the U.S. Social Security Administration list of most popular baby boy names.
Which undefined term is needed to define an angle? Plane Point Ray Line. Undefined, you need a line to define an angle (if you're looking for undefined terms). This is because, if you think about it, a ray is part of a line.
An instrument, usually half a circle or sphere, used to measure the field of vision. perimeter. An instrument for measuring the angular extent and the characteristics (e.g. presence of scotoma) of the visual field. See campimeter; visual field; isopter; tangent screen. arc perimeter Perimeter consisting of a semicircular arc, the inside surface of which is painted matt black or grey. The patient's head is placed such that the eye under investigation is located at the centre of curvature of the arc.