I once read a story that contained the phrase ‘a hare’s breath away’ from something, meaning a very short distance from it. It’s a lovely image, but hare’s breath is a mistaken form of the standard idiom hair’s breadth (a hair being extremely narrow). The writer probably heard the phrase before seeing it in print, and reinterpreted it. After all, both pairs of nouns – hare/hair and breath/breadth – are homophones (or near homophones), and hare’s breath makes a poetic kind of sense: the puff of air from a hare’s exhalation would not reach far.
This is a special type of error, known in linguistic circles as an eggcorn. You may have come across some before: intensive purposes (intents and purposes), pre-Madonna (prima donna), damp squid (damp squib), upmost (utmost), bread and breakfast (bed and breakfast), bonified (bona fide), peak your interest (pique your interest), mute point (moot point), old-timers’ disease (Alzheimer’s disease), gun-ho (gung-ho), firstable (first of all), tow the line (toe the line), wet your appetite (whet your appetite).
In each case, you can see how it could have happened. Whet is not a common or familiar verb, but wet is, and wet suggests the way your mouth waters or your stomach juices flow when you’re about to eat. So wet your appetite seems right. Gung-ho means ‘very enthusiastic, especially about something that might be dangerous’, but gung (from Chinese) is not a familiar morpheme in English, whereas gun is – and gun is strongly associated with danger. Hence gun-ho.
The Eggcorn Database is a wonderful website on this phenomenon, listing hundreds of eggcorns along with informed analysis and forum discussions. As Mairi MacDonald wrote in MED Magazine, ‘the database’s authors are not trying to force language into an artificial model, but rather, using it as a tool for observation’. There’s an entry for hare’s breath, as well as the rarer variant hare’s breadth and also hair’s breath.
Eggcorns are a type of folk etymology, the difference being that folk etymologies are more widespread. Penthouse, for example, has nothing to do with houses, etymologically – the word comes from Middle English pentis, from Old French apentiz – but that’s how people automatically, and understandably, reanalysed it. Whether it’s one or a million people who use it, the original impulse is the same: ‘to find meaningful parts in otherwise unparsable expressions’, as Arnold Zwicky put it.
In a similar vein there are also malapropisms, which tend not to be pronounced so closely or to make a certain sense in the way that eggcorns do. Mondegreens, meanwhile, are misheard song lyrics – I wrote about these here. The differences between them are described in this Language Log post, which also records the origins of the word eggcorn, which is itself an eggcorn: a misinterpretation of acorn. And you know what they say about little acorns.