Acute angle, § 27.
Adjacent angles, § 23.

diedral angles, § 428.
Alternate-exterior angles, § 71.
-interior angles, § 71.

Alternation, § 235.
Altitude of a cone, § 553.

of a cylinder, § 540.

of a frustum of a cone,
§ 553.

Apothem of a regular polygon,
§ 341.

Arc of a circle, § 142.
Area of a surface, § 302.
Axiom, § 15.

Axis of a circle of a sphere, § 567.
of a circular cone, § 553.

of a circular cylinder, § 546.
of symmetry, § 387.

of a polyedral angle, § 452.
of a pyramid, § 502.

of a spherical pyramid, § 589.
of a spherical sector, § 664.
of a spherical wedge, § 617.
of a triangle, § 60.
Bases of a cylinder, § 540.

of a parallelogram, § 104.
of a prism, § 466.

of a spherical segment, § 662.
of a trapezoid, § 104.

of a truncated prism, § 472.
of a truncated pyramid,
§ 505.

of a zone, § 662.
Bi-rectangular triangle, § 598.
Broken line, § 7.

Central angle, § 148.
Centre of a circle, § 142.

of a parallelogram, § 111.

of a regular polygon, § 341.

of a sphere, § 561.
of symmetry, § 386.