Suppletion

Definition
Suppletion is a phenomenon by which the addition of a semantic aspect or grammatical function is expressed by a totally or partially different morpheme which has little or no phonological connection with the base form.

Example
The alternation between the English verb go and its past tense form went is an example of total suppletion. The alternation between France and French is an example of partial suppletion.

Links

 * Utrecht Lexicon of Linguistics

Other Languages
German: Suppletion (de)