heterography 

the use of different letters or a group of letters to represent the same sound(s). Some of the examples of heterography are: sEw and sOw, bEAt and bEEt and rOUgh and rUff.

Heterography differs from homography (= use of the same spellings for words that have different meanings).

heterography by uttam maharjan December 1, 2010

heterograph 

a letter, or a group or sequence of letters, that is used to denote the same sound or sounds.

In the words 'beau', 'bow' and 'go', 'eau', 'ow' and 'o' are heterographs.

heterograph by uttam maharjan December 8, 2010