In linguistics and etymology, suppletion is the use as an inflected form of a word of an entirely different word that is not cognate to the uninflected form. Here are some examples:

• In English, the past tense of the verb go is went, which comes from the past tense of the verb wend, archaic in this sense. (The modern past tense of wend is wended.)

• In Germanic languages such as English, and in Romance languages, the comparative and superlative of the adjective "good" is suppletive; in English and the Romance languages, "bad" is also suppletive:

† This is an adverbial form ("badly"); the Italian adjective is itself suppletive (cattivo, akin to "captive").

• Similarly to the Italian noted above, the English adverb form of "good" is the unrelated word "well," from Old English wel, akin to wyllan "to wish."

• In English, the complicated irregular verb be / is / were has forms from several different roots: be originally comes from Indo-European *bhu-; am, is and are from *es-, and was and were from *wes-.

• Also in English, the word people is often used as the plural form of the unrelated word person (from the Latin words populus and persona, respectively.) The two exist as unrelated nouns, with the legalistic plural "persons" and the use of "people" as a singular noun to mean "ethnic group"; however, when "people" is used as the plural of "person," it takes a plural verb.

• In Italian, forms such as io vado, tu vai, lui va are part of the conjugation of the verb andare ("to go"). Compare the Spanish yo voy, tú vas, él va, nosotros vamos... (ir "to go") and yo ando, tú andas, él anda... (andar "to walk"), two separate verbs.

• Indeed, the verb "to go" has a variety of suppletive forms in Romance languages. Compare the following paradigms (the first three are from French):
  • the infinitive aller, and present nous allons, vous allez; (of obscure Latin origin, either from ambulare, "walk" or a backformation from allatus, past participle of afferre, "carry." Allatus from afferre is itself a suppletive form in Latin.)
  • the present je vais, tu vas, il va, ils vont; (from Latin vadere, "wander.")
  • the future j'irai, tu iras, il ira... and conditional j'irais etc.; (from Latin ire, "go")
  • and, in Spanish, the preterite yo fui, tú fuiste, él fue (identical to the preterite of ser "to be").