A & R Definition

A¹
a
noun As, A's, a's

1. The first letter of the English alphabet.
2a. music.
The sixth note on the scale of C major;
Form: A
2b. music.
The musical key which has this note as its base.
Form: A
3. Someone or something of first class, first in a sequence, or belonging to a class arbitrarily designated A.

Form: A (usually)
4. medicine.
One of the four blood types in the ABO blood group system.
5. The principal series of paper sizes, ranging from A0 (841 x 1189mm) to A10 (26 x 37mm).

Idiom: from A to B

From one place or point to another.

Idiom: from A to Z

From beginning to end.

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A²
abbreviation

1. Absolute (temperature).
2. cards.
Ace.
3. Acre or acres.
4. music.
Alto.
5. Ammeter.
6. Ampere or amperes.
7. Angstrom.
8. Area.
9. Argon.
10. Atomic weight.
11. IVR.
Austria.

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a¹
an
indefinite article

1. Used chiefly with a singular noun, usually where the thing referred to has not been mentioned before, or where it is not a specific example known to the speaker or listener. Compare the.
2. Used before a word describing quantity.

Example: a dozen eggs
3a. Any or every;

Example: A fire is hot
3b. Used after not or never: any at all.

Example: not a chance
4. Each or every; per.

Example: once a day
5. One of a specified type.

Example: He thinks he's a real Romeo

Etymology: Anglo-Saxon an one.

Info:

Some people use an before words beginning with a weakly sounded h, eg an hotel, an historic occasion. This use of an is no more nor less correct than a; however, it is sometimes regarded as old-fashioned.

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a²
abbreviation

1. Acceleration.
2. Acre or acres.
3. Adjective.
4. Are or ares.
5. Area.
6. ante (Latin), before.

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a³ A¹