What is the correct capitalisation of the word "sonar" (and why)?



SONAR was originally an acronym for "SO und N avigation A nd R anging", although in common usage sonar is acceptable, with Sonar appearing at the beginning of sentences.

  • 5
    I sometimes despair of these "What is the correct way..." questions. It wouldn't be so bad if they just asked "How do competent speakers/writers normally..." But of course you are completely "correct". By way of proof (if such were needed) here's what they actually write. Bearing in mind that the (already relatively low) usages of Sonar are artificially inflated by many occasions when it starts a sentence, sonar is the out-and-out winner! – FumbleFingers Jan 18 '12 at 23:57
  • Isn't sonar acceptable in 'non-common' usage? The dictionaries I've checked in don't indicate this. – Edwin Ashworth Dec 9 '15 at 17:02
  • My answer does say that :-) – tdc Dec 9 '15 at 20:40

The Chicago Manual of Style notes (emphasis mine):

Initialisms tend to appear in all capital letters, even when they are not derived from proper nouns (HIV, VP, LCD). With frequent use, however, acronyms—especially those of five or more letters—will sometimes become lowercase (scuba); those that are derived from proper nouns retain an initial capital.

"A Brief History of Active Sonar" (note the capitalization of sonar in title case; the same applies at the start of a sentence) documents that sonar was coined in 1942, following the pattern of radar.

It's instructive to note that the forerunner of the sonar was the ultrasonic ASDIC (Allied Submarine Detection Investigation Committee); asdic is listed as a synonym for sonar in British English.


Sonar has long been accepted as an ordinary word (since around 1979). So it should be capitalized only at the beginning of a sentence.


From the Guardian Style Guide:

abbreviations and acronyms

Use all capitals if an abbreviation is pronounced as the individual letters: BBC, VAT, etc; if it is an acronym (pronounced as a word) spell out with initial capital, eg Nasa, Nato, unless it can be considered to have entered the language as an everyday word, such as awol, laser and, more recently, asbo, pin number and sim card. Note that pdf and plc are lowercase.

So it's "Sonar", since it's an acronym -- or maybe "sonar" if you believe it has become an everyday word.

But the Guardian Style Guide is just one guide. Other publishers may have different guidelines.

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    All acronyms are abbreviations. In my 'lect, BBC and VAT are abbreviations but not acronyms, since they're pronounced letter-by-letter. A person who said VAT like "vat" would consider it an acronym (and also an abbreviation). So I disagree with @Pureferret pretty much completely. – Charles Jan 18 '12 at 17:03
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    @Pureferret: VAT is usually an initialisation; the BBC is always an initialisation, and not an acronym. Look up the definition of 'acronym'. – Marcin Jan 18 '12 at 17:04
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    @Pureferret: I don't know how you pronounce "BBC", but I've never met anyone who manages to pronounce it as anything other than a sequence of letters. – Marcin Jan 18 '12 at 17:11
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    @Pureferret: "Beeb" is not a pronunciation of "BBC", but a nickname. – Marcin Jan 18 '12 at 17:21
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    @slim: You may note that pureferret started this flight of pedantry. If we're going to suffer pedantry, it should at least be correct. – Marcin Jan 18 '12 at 17:23

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