1. [v]  divide (a disk) into marked sectors so that it may store data; "Please format this disk before entering data!"
2. [v]  assign an initial value to a compute program

INITIALISE is a 10 letter word that starts with I.

To give a variable its first value. This may be done automatically by some languages or it may require explicit code by the programmer. Some languages allow initialisation to be combined with variable definition, e.g. in c:

        int i = 0;

Failing to initialise a variable before using it is a common programming error, but one which compilers and automatic checkers like lint can easily detect.