The origin of the hyphen is not clear, but it is said that the widespread (not wide-spread, lesson one!) use was direct result of the invention of the printing press. When printing became common, printers needed a way to keep all the lines uniform, and hence often ran into the problem of having to split or separate words that would normally not be separated. One of the methods to split the words was to use a small dash. However, over a period of time the application of the hyphen has changed considerably.
A Little About the Hyphen
A hyphen is a punctuation mark that is used to join words or to separate syllables of a single word. Hyphens are often confused with dashes, which are longer and have various other uses. They can also be sometimes confused with the minus sign. The main difference between the hyphen and the dash, is that the hyphen is shorter than the dash. The use of hyphens is known as hyphenation. One of the basic rules is to not place spaces between a hyphen and either of the words it connects, except, when you are using a suspended hyphen. For example, "nineteenth- and twentieth-century writers". It is important to remember that not all of these rules are agreed upon universally, and different dictionaries may have their own versions.
When to Use a Hyphen
It should be used to join two or more words that serve as a single adjective preceding a noun. However, it is important to note that compound modifiers come after a noun, and should not be hyphenated.
Example: "chocolate-covered peanuts", and not "chocolate covered peanuts". The latter wouldn't refer to the specific peanuts covered with chocolate, but would generically imply that the peanuts are covered with chocolate.
A hyphen should be used to join compound numbers, but not when one of the words is on the lines of 'hundred', 'million', etc.
Example: twenty-four, thirty-three. If these words were to be written without the hyphen, the first number would, often nonsensically, become an adjective of number for the second number.
A hyphen is used along with prefixes like 'ex-', 'self-', 'pro-', 'anti-', etc., as well as with suffixes like '-elect', '-like', etc. Although nowadays many prefixes and suffixes are added without a hyphen, it is mandatory to use one when the noun is a proper noun.
Example: anti-American, mid-June, all-inclusive, ex-employer, President-elect, sand-like
A hyphen should be used to divide words at the end of a line, with the second part of the word following at the start of the next line. Such a break should only be made between syllables. If a word already contains a hyphen in it, the word shouldn't split according to syllables; end the line with the entire first word and the hyphen, and continue with the second word at the start of the next line.
Examples: sell-ing, indi-vidual, etc.
It can also be used for line breaks in words that end with '-ing'. The hyphen should be placed where a single final consonant in the root word is doubled before the use of the tense-denoting suffix '-ing'. If the word contains a double syllable at the end, hyphenate the suffix itself.
Examples: plan-ning, run-ing, call-ing, etc.
A hyphen can also be used to check whether a compound noun is actually two words, one word, or hyphenated. You will, however, have to check the dictionary to know whether you should treat the noun as separate nouns.
Examples: 'eyewitness' as opposed to 'eye-witness', 'eye-opener' as opposed to 'eyeopener', etc.
As is the case with compound nouns, it is the same with the compound verbs as well. You will have to look them up in the dictionary to know where they are to be hyphenated.
Examples: 'air-condition' is usually hyphenated, whereas ''downsize' usually isn't.
Spelled-out fractions should always be hyphenated. However, it is not necessary to use a hyphen if the fraction is being expressed as an actual share.
Examples: 'one-third' would require a hyphen, but 'a third' wouldn't.
There is a lot of debate about hyphens. Hence, you will have to refer to a reliable dictionary to know if the particular words are to be hyphenated.