an

andeterminer

An is the form of a used directly before a word that begins with a vowel sound; it introduces a person or thing as one example of its kind, without pointing to a particular, already-known one.

1. one, first mentionused before a singular countable noun beginning with a vowel sound, to talk about a person or thing without saying which one, especially the first time it is mentioned

   An is simply a used before a vowel sound: I saw an owl in the garden. Once the thing has been introduced this way, the usually takes over the next time it is mentioned: I saw an owl; the owl was gray.

   • I saw an owl in the garden last night.
   • Would you like an apple?
   • She works as an editor at a small company.
   • There's an email for you from Yuki.

   Compare a (a is used instead directly before a consonant sound); the (the is used instead once the listener already knows which one is meant)

2. any one, in generalused before a singular countable noun beginning with a vowel sound to make a general statement about every member of a kind

   This use talks about the whole kind, not one particular example: an elephant never forgets means every elephant.

   • An octopus has eight arms.
   • An honest answer is always better than a clever excuse.
   • An umbrella is useful on a rainy day.

3. each, perused after a number or amount and before a noun of time or measurement beginning with a vowel sound, to mean each or every

   This use gives a rate: how often, how much, or how fast something happens: fifty miles an hour, once an evening.

   • The car was going almost eighty miles an hour.
   • Ravi checks his phone about once an hour.
   • The parking garage charges five dollars an hour.

   Collocations

   phrase fifty miles an hour, once an evening, two dollars an item