plural a's or as
ˈāz 
often capitalized, 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
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
capitalized
: 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
1
—used as a function word before singular nouns when the referent is unspecified
a man overboard
and before number collectives and some numbersa dozen
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 man who was here yesterday
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 bronze made in ancient times
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
Christmas 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
Margaret Carlson4
—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)
Psalms 127:3 (King James Version)
ə,
also
(ˈ)ā
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 wordAuli'i Cravalho, quoted in The New York TimesBut I did kinda sorta secretly hope to one day be interviewed from Oprah Winfrey's yoga nook.—Jennifer Senior
Jennifer SeniorThat's a whole lotta [=lot of] hypothesizin' without a whole lotta science.—Rebecca Watson
Rebecca Watson
archaic
: have
I might a had husbands afore now …—John Bunyan
John BunyanPoor 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
Anne Newport Royall1
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
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
(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 hachromatic
ahistorical
anastigmatic
anhydrous
: replacing carbon especially in a ring
aza-
ə
: oxide
silica
alumina
magnesia
1
ace
2
adenine
3
ampere
argon
angstrom
Cite this Entry
“A.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/a. Accessed 4 Nov. 2025.
Copy CitationKids Definition
a
1 of 5 noun
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
3 of 5 preposition
ə
(ˈ)ā
: in each : to each : for each
twice a week
one a piece
a-
4 of 5 prefixə
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 hanhydrate
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 abbreviation1
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
: 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 abbreviation1
adenine
2
ampere
Å
4 of 4 symbol
angstrom
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