Some words in English, such as enquire and inquire, can be spelled with either en— or in–. In fact, from a historical point of view, these two prefixes are the same. As the Latin language developed into French, Latin in— became en–. For example, Latin inflammāre developed into French enflammer, borrowed into English as enflame. Later the word came to be written as inflame in imitation of the original Latin form. During the middle English period, a great number of French words beginning with en— came into the English language, and in many instances the spelling of these words was similarly remodeled to begin with in–. In some pairs of words, however, the difference in spelling between en— or in— has been used to distinguish a difference in meaning, such as in the pair ensure and insure. Because of the difference in spelling, most English speakers today probably consider ensure and insure to be two entirely different verbs, but in origin insure is just a specialized financial use of the word ensure, “make secure.”
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