There are 3 definitions of an in English:

an1

Syllabification: an
Pronunciation: /an
 
, ən
 
/

determiner

The form of the indefinite article (see a1) used before words beginning with a vowel sound.

Usage

Is it ‘a historical document’ or ‘an historical document’? ‘A hotel’ or ‘an hotel’? There is still some divergence of opinion over which form of the indefinite article should be used before words that begin with h- and have an unstressed first syllable. In the 18th and 19th centuries, people often did not pronounce the initial h for these words, and so an was commonly used. Today the h is pronounced, and so it is logical to use a rather than an. However, the indefinite article an is still encountered before the h in both British and American English, particularly with historical: in the Oxford English Corpus around a quarter of examples of historical are preceded with an rather than a.

Definition of an in:

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Word of the day hubris
Pronunciation: ˈ(h)yo͞obris
noun
excessive pride or self-confidence

There are 3 definitions of an in English:

an-2

Syllabification: an-

prefix

Variant spelling of ad- assimilated before n (as in annihilate, annotate).

Definition of an in:

There are 3 definitions of an in English:

an-3

Syllabification: an-

prefix

Variant spelling of ana- shortened before a vowel (as in aneurysm).

Definition of an in: