early 17th century: via late Latin from Greek huphen 'together', from hupo 'under' + hen 'one'
In modern English the use of hyphens is in general decreasing, especially in compound nouns: website is preferred to web-site, and air raid to air-raid. Hyphens are still often employed where a compound expression precedes a noun, as in first-rate musicians or twenty-odd people (twenty odd people means something quite different!), but even in this context there is a growing trend to omit them. When a phrasal verb such as build up is made into a noun it is usually hyphenated (a build-up of pressure). Note, however, that a normal phrasal verb should not be hyphenated: write food to take away not food to take-away, and continue to build up your pension not continue to build-up your pension.