a

1 of 13

noun

ˈā 

variants often A

plural a's; often A's or as; often As ˈāz 

often attributive

1

a

: the 1st letter of the English alphabet

b

: a graphic representation of this letter

c

: a speech counterpart of orthographic a

… the so-called Boston pronunciation, with its broad a's …

—H. L. Mencken

2

: the sixth tone of a C-major scale

3

: a graphic device for reproducing the letter a

4

: one designated a especially as the first in order or class

5

a

: a grade rating a student's work as superior in quality

b

: one graded or rated with an A

6

: something shaped like the letter A

7

A : the one of the four ABO blood groups characterized by the presence of antigens designated by the letter A and by the presence of antibodies against the antigens present in the B blood group

a

2 of 13

indefinite article

ə

for emphasis

(ˈ)ā 

Canadian

ˈa 

1

—used as a function word before singular nouns when the referent is unspecified

A man walked by.

heard a shout

and before number collectives and some numbers

a dozen

a thousand

2

: the same

birds of a feather

swords all of a length

3

a

—used as a function word before a singular noun followed by a restrictive modifier

a person who saw it happen

b

: any

a person who is sick can't work

c

—used as a function word before a mass noun to denote a particular type or instance

a plastic used in packaging

d

—used as a function word before a proper noun representing an example or type

the attractions of a Boston or a Cleveland

e

—used as a function word before a proper noun to indicate limited knowledge about the referent

A Mr. Smith called to inquire about the job.

f

—used as a function word before a proper noun to distinguish the condition of the referent from a usual, former, or hypothetical condition

A triumphant Ms. Jones greeted her supporters.

g

—used before the name of a day of the week to refer to one occurrence of it

My birthday falls on a Tuesday this year.

h

—used before the name of a person (such as a famous artist) when the name is being used to refer to something (such as a painting) created by that person

Her violin is a Stradivarius.

i

—used before a family name to show that someone is a member of that family

To be a Kennedy is to lead two lives …

—Margaret Carlson

4

—used as a function word with nouns to form adverbial phrases of quantity, amount, or degree

felt a bit tired

A vs. an: Usage Guide

In speech and writing a is used before a consonant sound.

a door

a human

Before a vowel sound an is usual

an icicle

an honor

but especially in speech a is used occasionally, more often in some dialects than in others.

a apple

a hour

a obligation

Before a consonant sound represented by a vowel letter a is usual

a one

a union

but an also occurs though less frequently now than formerly.

an unique

such an one

Before unstressed or weakly stressed syllables with initial h both a and an are used in writing.

a historic

an historic

In the King James Version of the Old Testament and occasionally in writing and speech an is used before h in a stressed syllable.

an huntress

an hundred

children are an heritage of the Lord

—Psalms 127:3 (King James Version)

a

3 of 13

preposition (1)

ə

also

(ˈ)ā 

1

: in, to, or for each

twice a week

2

chiefly dialectal : on, in, at

a

4 of 13

preposition (2)

ə

informal

: of

There are a lot a stairs, but the view at the top is absolutely beautiful.

—Auli'i Cravalho, quoted in The New York Times

—often attached to the preceding word

But I did kinda sorta secretly hope to one day be interviewed from Oprah Winfrey's yoga nook.

—Jennifer Senior

That's a whole lotta [=lot of] hypothesizin' without a whole lotta science.

—Rebecca Watson

a

5 of 13

verb

ə, 

(ˌ)a 

archaic

: have

I might a had husbands afore now …

—John Bunyan

Poor Sir William! never shall I forget how he looked whin my lady and he parted. I could a tould the reason, but I'd a cut my tongue out first.

—Anne Newport Royall

a

6 of 13

abbreviation (1)

1

absent

2

acceleration

3

acre

4

adult

5

alto

6

chemistry amorphous

—usually used in combination

a-Si

7

anode

8

answer

9

ante

10

anterior

11

are

12

area

13

atto-

14

author

a-

7 of 13

prefix (1)

ə

1

: on : in : at

abed

2

: in (such) a state or condition

afire

3

: in (such) a manner

aloud

4

: in the act or process of

gone a-hunting

atingle

a-

8 of 13

prefix (2)

(ˈ)ā

also (ˈ)a

or (ˈ)ä

variants or an-

(ˈ)an

: not : without

asexual

—a- before consonants other than h and sometimes even before h, an- before vowels and usually before h

achromatic

ahistorical

anastigmatic

anhydrous

-a-

9 of 13

combining form

: replacing carbon especially in a ring

aza-

-a

10 of 13

noun suffix

ə

: oxide

silica

alumina

magnesia

A

11 of 13

abbreviation (2)

1

ace

2

adenine

3

ampere

A

12 of 13

symbol

argon

Å

13 of 13

abbreviation (3)

angstrom

Examples of a in a Sentence

Noun

a word that begins with an a

a word that begins with a

a song in the key of A

She got an A on the exam.

Recent Examples on the Web

Preposition

Spaceflight caused a 20% reduction in chlorophyll a, the main pigment involved in photosynthesis, but the spores seemed to be healthy despite that drop, the team found. —Mike Wall, Space.com, 22 Nov. 2025

Word History

Etymology

Indefinite article

Middle English, from Old English ān one — more at one

Preposition (1)

Middle English, from Old English a-, an, on

Preposition (2)

Middle English, by contraction

Verb

Middle English, contraction of have

Prefix (1)

Middle English, from Old English

Prefix (2)

Latin & Greek; Latin, from Greek — more at un-

Combining form

perhaps from -a- in ring compounds such as thiazole (in which -a- is the initial of azole)

Noun suffix

New Latin, from -a (as in magnesia)

First Known Use

Noun

before the 12th century, in the meaning defined at sense 1a

Indefinite Article

before the 12th century, in the meaning defined at sense 1

Preposition (1)

before the 12th century, in the meaning defined at sense 2

Preposition (2)

15th century, in the meaning defined above

Verb

14th century, in the meaning defined above

Kids Definition

a

1 of 5 noun

ˈā 

plural a's or as

often capitalized

1

: the first letter of the English alphabet

2

: a musical note referred to by the letter A : the sixth tone of a C-major scale

3

: a grade rating a student's work as superior

a

2 of 5 indefinite article

ə 

(ˈ)ā

1

: someone or something unspecified

a man in the street

a dozen

2

: the same : one

two of a kind

birds of a feather

3

: of whatever kind : any

a student who works hard

—used in all senses before words beginning with a consonant sound compare an

a

3 of 5 preposition

ə 

(ˈ)ā

: in each : to each : for each

twice a week

one a piece

a-

4 of 5 prefix

ə

1

: on : in : at

abed

2

: in a specified state or condition

afire

3

: in a specified manner

aloud

4

: in the act or process of

gone a-hunting

a-

5 of 5 prefix

(ˈ)ā

variants or an-

(ˈ)an

: not : without

asexual

—a- before consonants other than h and sometimes before h, an- before vowels and usually before h

anhydrate

Etymology

Indefinite article

Old English ān "one"

Preposition

Old English a-, an, on "on"

Prefix

Old English a- "on, in, at"

Prefix

Greek a-, an- "not"

Medical Definition

a

1 of 4 abbreviation

1

about

2

absent

3

absolute

4

absorbency; absorbent

5

accommodation

6

acetum

7

acid; acidity

8

actin

9

active; activity

10

allergist; allergy

11

alpha

12

anode

13

answer

14

ante

15

anterior

16

aqua

17

area

18

artery

19

asymmetric; asymmetry

A

2 of 4 noun

ˈā 

: the one of the four ABO blood groups characterized by the presence of antigens designated by the letter A and by the presence of antibodies against the antigens present in the B blood group

A

3 of 4 abbreviation

1

adenine

2

ampere

Å

4 of 4 symbol

angstrom