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Abbreviations and a/an/the: Acronyms vs. initialisms

Most people can identify abbreviations in general. Red Pen Bristol (RPB) identifies two types of abbreviations: acronyms and initialisms.

Although sometimes dictionaries can disagree a little about exactly how these two types of abbreviations are related, RPB views them as two distinct categories.

Acronyms are abbreviations pronounced like a word:


NASA (National Aeronautics and Space Administration)

NATO (North Atlantic Treaty Organization)

WHO (World Health Organization)


Initialisms are abbreviations in which each letter is pronounced:


NSA (National Security Agency)

FBI (Federal Bureau of Investigation)

UFO (Unidentified Flying Object)

BBC (British Broadcasting Corporation)


That’s why “a NASA representative” would consult with “an NSA representative”. Remember that pronunciation determines your indefinite article (‘a’ or ‘an’)! While NASA starts with a hard ‘nah’ sound (a consonant), NSA technically starts with a vowel sound (‘e’).


That’s also why you’d say “Visit WHO’s website” versus “Call the FBI about the UFO". Think of it this way: Acronyms are like names. My name is Jessica. You would never say, “If you need editing, email the Jessica.” You would just say, "Email Jessica."


Of course, this is English: There are always some exceptions. But distinguishing acronyms and initialisms can help a lot in day-to-day drafting.