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English definition of “a”

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a

determiner uk   weak /ə/ strong // us    /ə/  // ( also an)

a determiner (NOT PARTICULAR)

A1 used before a noun to refer to a single thing or person that has not been mentioned before, especially when you are not referring to a particular thing or person: I've bought a car. She's got a boyfriend. There was a sudden loud noise. What a shame that you couldn't go to the party. I heard a child crying. Is he a friend of yours (= one of your friends)?A1 used to say what type of thing or person something or someone is: She wants to be a doctor when she grows up. This is a very mild cheese. Experts think the painting may be a Picasso (= by Picasso).A1 used to mean any or every thing or person of the type you are referring to: Can you ride a bike? A cheetah can run faster than a lion. A teacher needs to have a lot of patience. used before some uncountable nouns when you want to limit their meaning in some way, such as when describing them more completely or referring to one example of them: I only have a limited knowledge of Spanish. He has a great love of music. There was a fierceness in her voice.A2 used before some nouns of action when referring to one example of the action: Take a look at this, Jez. I'm just going to have a snack. There was a knocking at the door.A2 used when referring to a unit or container of something, especially something you eat or drink: I'd love a coffee. All I had for lunch was a yogurt.A2 used before the first but not the second of two nouns that are referred to as one unit: a cup and saucer a knife and forkA2 used before some words that express a number or amount: a few days a bit of wool a lot of money used in front of a person's name when referring to someone who you do not know: There's a Ms Evans to see you. used in front of someone's family name when they are a member of that family: Is that a Wilson over there? used before the name of a day or month to refer to one example of it: My birthday is on a Friday this year. It's been a very wet June.
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a determiner (ONE)

A1 one: a hundred a thousand a dozen There were three men and a woman.A2 used between a fraction and a unit of measurement: half a mile a quarter of a kilo three quarters of an hour six tenths of a secondA2 used when saying how often something happens in a certain period: Take one tablet three times a day. I swim once a week.A2 used when saying how much someone earns or how much something costs in a certain period: She earns $100,000 a year. My plumber charges £30 an hour. I pay £25 a week for my parking permit.
(Definition of a determiner from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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