Hyphens are commonly used to join two or more associated words when no single word exists, for instance ‘on-site’, ‘stress-free’ or ‘mother-in-law’.
The interesting thing about them is that having done their job they are often discarded over time and – ta da! – a new word is born some years later, unencumbered by punctuation. We have seen this happen with words such as ‘book-seller’, ‘life-like’ and ‘pre-historic’, which are rarely, if ever, hyphenated today.
Unfortunately, the evolutionary process from two or more unconnected words to hyphenated words to single words is not consistent and there is no hard and fast rule governing when words should remain separate, be hyphenated or merged into a single word, which can lead to confusion.
One consistent practice though is the use of hyphens to avoid visually disconcerting cases of ‘letter collision’ so that we have ‘shell-like’ (rather than ‘shelllike’), semi-illiterate (instead of the confusing ‘semiilliterate’) and ‘de-ice’ (not ‘deice’).
