A compound word is a word made up from two or more other words joined together. They are often created to describe a new concept or idea and are thus neologisms‏‎.

As a simple example, take the words foot and ball. These were brought together to describe the game: football. Likewise the following are just a few of the many, many compound words in English:

eyesight, airport, overtake, earthworm, homework, brainwash…

Compound Word Development

There is usually a set pattern to the development of compound words. When a new concept needs to be described we can use two existing words to do so. For example:

The enemy counter attacked.

If this pairing of words becomes common then people may well start to associate them even more closely with a hyphen:

The enemy counter-attacked.

Finally, if the usage becomes even more common the hyphen is dropped and the two words become one:

The enemy counterattacked.

Types of Compound Words

Compound words can be made up and be part of different parts of speech‏‎:

Compound Nouns are nouns made up of two words which can be of many different word classes, e.g.

finger + print = fingerprint = {noun} + {noun}

black + board = blackboard = {adjective} + {noun}

in + put = input = {preposition} + {verb}

Compound Adjectives are adjectives‏‎ made up of two or more words. They are becoming more prevalent these days and are often used as marketing gimmicks:

That must-have accessory for Summer.

The new pay-as-you-go mobile phone tariff.

Note that just using two adjectives together does not create a compound word; compound words are used to describe new concepts or ideas. Likewise a compound verb is similar to a verb phrase and does is not really classed as a compound word.

To Hyphenate or Not to Hyphenate?

Whether to use a hyphen or not is often a matter of style and there is no universal agreement on this. Some words have for some reason been very reluctant to drop the hyphen whilst others seem awkward when it appears:

The middle-aged lady with her teenage son.

* The middleaged lady with her teen-age son.

* Asterisks are used to denote ungrammatical or questionable sentences.

Thus if you are in doubt about whether to hyphenate or not, use a dictionary!