AD

UK: 'AD': /ˌeɪˈdiː/; 'ad': /ˈæd/ US: /æd/ ,(ad)

Collins Concise English Dictionary © HarperCollins Publishers::

AD abbreviation

1. (indicating years numbered from the supposed year of the birth of Christ) anno Domini: 70 ad
   Compare BC

Etymology: (sense 4) Latin: in the year of the LordIn strict usage, ad is only employed with specific years: he died in 1621 ad, but he died in the 17th century (and not the 17th century ad). Formerly the practice was to write ad preceding the date ( ad 1621), and it is also strictly correct to omit in when ad is used, since this is already contained in the meaning of the Latin anno Domini (in the year of Our Lord), but this is no longer general practice. bc is used with both specific dates and indications of the period: Heraclitus was born about 540 bc; the battle took place in the 4th century bc

WordReference Random House Learner's Dictionary of American English © 2025

ad¹ /æd/   n. [countable]

1. an advertisement.

adj. [before a noun]

2. advertising:
   an ad agency.

A.D. or AD,an abbreviation of

1. Pronouns Latin anno Domini : in the year of the Lord;
   since Christ was born (used with dates): Charlemagne was born in a.d. 742.

WordReference Random House Unabridged Dictionary of American English © 2025

ad¹  (ad), n. 

1. advertisement.
2. advertising:
   an ad agency.

• by shortening 1835–45

ad²  (ad), n. [Tennis.]

1. Sport advantage (def. 5).
2. Sport ad in, the advantage being scored by the server.
3. Sport ad out, the advantage being scored by the receiver.

• by shortening 1945–50

ad³  (ad), prep. 

1. (in prescriptions) to;
   up to.

• Latin

ad-, 

1. a prefix occurring in loanwords from Latin, where it meant "toward'' and indicated direction, tendency, or addition:
   adjoin.
   Usually assimilated to the following consonant;
   see a-⁵, ac-, af-, ag-, al-, an- ², ap-¹, ar-, as-, at-. 

• Latin ad, ad- (preposition and prefix) to, toward, at, about; cognate with at¹

-ad¹ ,

1. a suffix occurring in loanwords from Greek denoting a group or unit comprising a certain number, sometimes of years:
   dyad; triad.
2. a suffix meaning "derived from,'' "related to,'' "concerned with,'' "associated with'' (
   oread
   ), introduced in loanwords from Greek (
   Olympiad; oread
   ), used sporadically in imitation of Greek models, as
   Dunciad,
   after
   Iliad.

• Greek -ad- (stem of -as), specialization of feminine adjective-forming suffix, often used substantively

-ad² ,

1. var. of -ade ¹:
   ballad.

-ad³ ,

1. [Anat., Zool.] a suffix forming adverbs from nouns signifying parts of the body, denoting a direction toward that part:
   dextrad;
   dorsad;
   mediad.

• Latin ad toward, anomalously suffixed to the noun; introduced as a suffix by Scottish anatomist John Barclay (1758–1826) in 1803

ad., 

1. Grammar adverb.
2. Business, advertisement.

A.D., 

1. active duty.
2. Pronouns in the year of the Lord;
   since Christ was born:
   Charlemagne was born in a.d. 742.
• Latin annō Dominī
3. art director.
4. Government assembly district.
5. assistant director.
6. athletic director.
7. average deviation.
Usage
Because anno Domini means "in the year of the Lord,'' its abbreviation a.d. was originally placed before rather than after a date:
The Roman conquest of Britain began in
a.d. 43 (or began a.d. 43). In edited writing, it is still usually placed before the date. But, by analogy with the position of b.c. "before Christ,'' which always appears after a date (Caesar was assassinated in 44 b.c.), a.d. is also frequently found after the date in all types of writing, including historical works:
The Roman emperor Claudius I lived from 10
b.c. to 54 a.d. Despite its literal meaning, a.d. is also used to designate centuries, being placed after the specified century:
the second century
a.d.

a.d., 

1. after date.
2. before the day.
• Latin ante diem
3. autograph document.

Collins Concise English Dictionary © HarperCollins Publishers::

ad / æd/ noun

1. short for advertisement

ad / æd/ noun

1. short for advantage

Collins Concise English Dictionary © HarperCollins Publishers::

ad- prefix

1. to; towards: adsorb, adverb
2. near; next to: adrenal

Etymology: from Latin: to, towards. As a prefix in words of Latin origin, ad- became ac-, af-, ag-, al-, an-, acq-, ar-, as-, and at- before c, f, g, l, n, q, r, s, and t, and became a- before gn, sc, sp, st