Geometry glossary: points, lines, angles, triangles, figures
Named definitions from point and line to circles, tangents, triangles and quadrilaterals, each with a drawn figure
Headed 'In geometry,' this page is an illustrated glossary of elementary geometry, each term paired with a small drawn figure. Leonardo lists the point, kinds of line (parallel, concurrent, straight, curved), the surface, and a full range of angles (rectilinear, right, curvilinear, obtuse, acute). He then defines circle terms (circumference, diameter, semicircle, major and minor portions, tangent line, arc, chord, tangent circles, sector), the three triangles by sides and by angles, and quadrilaterals including the square, tetragonism, and the rhombus he names by the Arabic term Elmuachin, closing that all other figures are called irregular.
On this page
Point, kinds of line, and surface
The list opens with the point, then the line and its varieties: equidistant or parallel, concurrent, straight and curved, followed by the surface. Each is set beside its drawn sign.
Angles: rectilinear, right, curvilinear, obtuse, acute
Leonardo defines the angle in general, then the rectilinear angle, the right angle (with its perpendicular), the curvilinear angle, and the obtuse and acute angles. Small wedge figures illustrate each.
Circle terms: diameter, semicircle, tangent, chord, sector
Circle vocabulary follows: circumference and diameter, semicircle, minor and major portions, tangent line, arc, chord, and circles tangent to one another, plus the sector and the angle at the center. Drawn circles accompany the terms.
Triangles by sides and by angles
The triangles are named: Ysopleuro (equilateral) of three equal sides, Ysocele (isosceles) of two, Scalene of three unequal; then Orthogoneo with one right angle, Ambligono with an obtuse, and Oxigoneo with three acute angles.
Quadrilaterals: square, rhombus (Elmuachin), and irregular figures
The four-sided figures include the square (four equal sides, four right angles), tetragonism, Elmuachin (four equal sides, four unequal angles) and a figure similar to it. Leonardo closes that all other figures are called irregular, drawing a few beside the note.