This list contains acronyms, initialisms, and pseudo-blends that begin with the letter A.

For the purposes of this list:

• acronym = an abbreviation pronounced as if it were a word, e.g., SARS = severe acute respiratory syndrome, pronounced to rhyme with cars
• initialism = an abbreviation pronounced wholly or partly using the names of its constituent letters, e.g., CD = compact disc, pronounced cee dee
• pseudo-blend = an abbreviation whose extra or omitted letters mean that it cannot stand as a true acronym, initialism, or portmanteau (a word formed by combining two or more words).

(a) = acronym, e.g.: SARS – (a) severe acute respiratory syndrome

(i) = initialism, e.g.: CD – (i) compact disc

(p) = pseudo-blend, e.g.: UNIFEM – (p) United Nations Development Fund for Women

(s) = symbol (none of the above, representing and pronounced as something else; for example: MHz – megahertz)

Some terms are spoken as either acronym or initialism, e.g., VoIP, pronounced both as voyp and V-O-I-P.

(Main list of acronyms)

• a – (s) Atto-
• A – (s) Ampere