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or A

noun pl. A's , a's

the first letter of the English alphabet: from the Greek alpha, a borrowing from the Phoenician
any of the speech sounds that this letter represents, as, in English, the vowel (a) of hat, (ä) of father, (ā) of bake, or (ô) of call
a type or impression for a or A
the first in a sequence or group
an object shaped like

adjective

of a or A
first in a sequence or group
shaped like

adjective, indefinite article

one; one sort of: we planted a tree
each; any one [a gun is dangerous]: a connotes a thing not previously noted or recognized, in contrast with the, which connotes a thing previously noted or recognized

to each; in each; for each; per: once a day

or a'

adjective

Scot. all

about
absent
Physics acceleration
active
adjective
adult
alto
anonymous
answer
are (unit of area)
atto-

noun

a blood type
☆ Educ. a grade indicating excellence: an A in history
Music
1. the sixth tone or note in the ascending scale of C major
2. a key, string, etc. producing this tone
3. the scale having this tone as the keynote

adjective

first-class; A 1

Physics absolute
adenine
America(n)
ampere
analog
angstrom
also Å
anode
answer
April
Chem., Archaic argon
Baseball, Basketball, Hockey assist(s)
attendance
August

See a in American Heritage Dictionary 4

or A (ā)

noun pl. A's a's or A's also as or As

The first letter of the modern English alphabet.
Any of the speech sounds represented by the letter a.
The first in a series.
Something shaped like the letter A.
A The best or highest in quality or rank: grade A milk.
Music
a. The sixth tone in the scale of C major or the first tone in the relative minor scale.
b. A key or scale in which A is the tonic.
c. A written or printed note representing this tone.
d. A string, key, or pipe tuned to the pitch of this tone.
A One of the four major blood groups in the ABO system. Individuals with this blood group have the A antigen on the surface of their red blood cells, and the anti-B antibody in their blood serum.

(ə; ā when stressed)

indef.art.

Used before nouns and noun phrases that denote a single but unspecified person or thing: a region; a person.
Used before terms, such as few or many, that denote number, amount, quantity, or degree: only a few of the voters; a bit more rest; a little excited.
a. Used before a proper name to denote a type or a member of a class: the wisdom of a Socrates.
b. Used before a mass noun to indicate a single type or example: a dry wine.
The same: birds of a feather.
Any: not a drop to drink.

Usage Note: In writing, the form a is used before a word beginning with a consonant sound, regardless of its spelling (a frog, a university). The form an is used before a word beginning with a vowel sound (an orange, an hour). • An was once a common variant before words beginning with h in which the first syllable was unstressed; thus 18th-century authors wrote either a historical or an historical but a history, not an history. This usage made sense in that people often did not pronounce the initial h in words such as historical and heroic, but by the late 19th century educated speakers usually pronounced initial h, and the practice of writing an before such words began to die out. Nowadays it survives primarily before the word historical. One may also come across it in the phrases an hysterectomy or an hereditary trait. These usages are acceptable in formal writing.

(ə)

preposition

In every; to each; per: once a month; one dollar a pound.

(ə)

aux.v.
Informal

Have: He'd a come if he could.

abbreviation