Definition of an:

part of speech: conjunction

Noting a single individual, but less emphatic than one; the indefinite article, put before nouns or adjs. in the sing. beginning with a vowel or the sound of a vowel- as, an egg, an honourable man.

Usage examples:

Word of the day

oil nut

The butter- nut of N. Amer,; a shrub; the Palma Christi. ...