Answer:
A diagonal is a straight line from a vertex of a polygon to
any other vertex of the polygon not next to it.
For
example,
There are two diagonals from A in the pentagon namely
AC and AD. The word diagonal derives from the Greek, later
adopted into Latin as diagonus (slanting line).
In
mathematics, in addition to its geometric meaning, a diagonal
is also used in matrices to refer to a set of entries along
a diagonal line.
