suppletive

See also: supplétive

English

suppletive ‎(comparative more suppletive, superlative most suppletive)

(grammar) Inflected by substituting an unrelated form (for example, in English, the adjectival forms good, better, best).
When "went" replaced "gang", "go" became suppletive.
Supplying deficiencies; supplementary; suppletory.

grammar

suppletive