Book IV Definitions

Euclid's Elements Book IV DEFINITIONS
1.	A rectilineal figure is said to be inscribed in a rectilineal figure when the respective angles of the inscribed figure lie on the respective sides of that in which it is inscribed.
2.	Similarly a figure is said to be circumscribed about a figure when the respective sides of the circumscribed figure pass through the respective angles of that about which it is circumscribed.
3.	A rectilineal figure is said to be inscribed in a circle when each angle of the inscribed figure lies on the circumference of the circle.
4.	A rectilineal figure is said to be circumscribed about a circle when each side of the circumscribed figure touches the circumference of the circle.
5.	Similarly a circle is said to be inscribed in a figure when the circumference of the circle touches each side of the figure in which it is inscribed.
6.	A circle is said to be circumscribed about a figure when the circumference of the circle passes through each angle of the figure about which it is circumscribed.
7.	A straight line is said to be fitted into a circle when its extremities are on the circumference of the circle.
Contents and Introduction Book IV Propositions

Euclid's Elements