an 1 (ən; ăn when stressed)
[Middle English, from Old English ān, one; see oi-no- in the Appendix of Indo-European roots.]
Word History: The forms of the indefinite article are good examples of what can happen to a word when it becomes habitually pronounced without stress. An is in fact a weakened form of one; both an and one come from Old English ān, "one." In early Middle English, besides representing the cardinal numeral "one," ān developed the special function of indefinite article, and in this role the word was ordinarily pronounced with very little or no stress. Sound changes that affected unstressed syllables elsewhere in the language affected it also. First, the vowel was shortened and eventually reduced to a schwa (ə). Second, the n was lost before consonants. This loss of n affected some other words as well; it explains why English has both my and mine, thy and thine. Originally these were doublets just like a and an, with mine and thine occurring only before vowels, as in Ben Jonson's famous line "Drink to me only with thine eyes." By the time of Modern English, though, my and thy had replaced mine and thine when used before nouns (that is, when not used predicatively, as in This book is mine), just as some varieties of Modern English use a even before vowels (a apple).
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.