Hyphenations and compounded words are my biggest weakness. I never know when I am supposed to compound, hyphenate, or just leave a space between two words. Thankfully, the “Merriam-Webster’s Concise Handbook for Writers” breaks it down nicely. It all has to do with whether the words are nouns, verbs, adjectives, etc. I have covered some examples of compounded nouns here.

Compounding Two Nouns
–In common usage short nouns where the first word is stressed the two nouns are written as one word. Ex. paycheck and football.
-In two nouns where both words are equally stressed the two nouns are spaced apart. Ex. desk lamp.
-In two nouns where the words are longer are generally spaced apart. Ex. computer desk.
–When two nouns function as a double title they are usually separated by a hyphen or slash. Ex. secretary-treasurer or bar-restaurant.
–When a noun or adjective are followed by man, woman, person, or people the words are usually written as one word. Ex. congressman, sales people.
–Units of measurement are usually separated with a hyphen. Ex. light-year, kilowatt-hour.

Compounding an Adjective and a Noun
-In most cases an adjective and noun are written as two separate words. Ex. minor league, genetic code. However, if the two words are short and the first word is stressed, they may be written as one word or hyphenated. Ex. notebook, two-step.
–Likewise, a noun followed by an adjective can be written apart or hyphenated. ex. sum total, president-elect.

Compounding a Participle and Noun
–Almost all participle and noun combinations are written as two words. Ex. frying pan, barbed wire.

Compounding Possessive Nouns with Nouns
–In most cases, a possessive now followed by a noun are written as two words. But occasionally they are hyphenated or written as one word without the apostrophe. Ex. hornet’s nest, bull’s-eye or bulls-eye, menswear.

Compounding a Noun with a Verb ending in –er or –ing
–Most nouns followed by a verb ending in –er or –ing are written as two words but sometimes hyphenated or sometimes as a single word. Ex. problem solver, air conditioner, fund-raiser, lifesaving.

Compounding Object Nouns and Verbs
–There is no hard and fast rule for compounding objects nouns with a verb. It could be written as two words, hyphenated, or compounded into one word. Ex. fish fry, eye-opener, roadblock.
–However, if you have a verb followed by an object noun they are almost always written as one word. Ex. cutthroat, pickpocket.

Compounding a Particle and a Noun
–A particle (preposition or adverb) followed by a noun is generally written as one word. Ex. undertone, input.

Compounding a Letter and a Noun
When combining a letter with a noun, the compound can either be written separately or with a hyphen. Ex. B vitamin, T-shirt, e-mail.

These are just a few examples of compounding nouns. As you have noticed there is not always a hard and fast rule. If you are not sure and the “Merriam-Webster’s Concise Handbook for Writers” does not cover it, try looking in the dictionary. If two compounded words are generally written as one word, they are likely to be in the dictionary. The dictionary sometimes indicates hyphenated words as well.