What is a Hyphen?

Hyphens are used to form a compound word. A compound word is the joining of two separate words to form one concept. Hyphens should be used when there is a compound adjective directly before the noun that it describes. There are other times in which a hyphen is needed such as brother-in-law or other family members that follow that example. Many two-digit numbers also require the use of a hyphen, such as twenty-four. Any words including self or ex should also be hyphenated.


There is a progression in the spelling of a compound. Many times, it starts out as two words, becomes joined with a hyphen, and then becomes one word. Therefore, it is very important to consult a recent dictionary or online resource to determine how a compound should be spelled. Remember, just because you joined a compound with a hyphen in one instance, that doesn’t mean you will always use a hyphen to join that compound.

It’s important to evaluate a compound on a case-by-case basis to determine if the use of a hyphen is necessary. I’m going to break down for you some of the most common instances when you should use hyphens. You should use a hyphen to join a compound when it is a compound adjective directly before the noun it describes. Here’s a prime example: “He wore a mud-stained shirt.” Here, “mud-stained” is a compound adjective right before the noun it describes, which is “shirt”. If I were to say to you, “His shirt is mud stained,” it would not need a hyphen. “Mud stain” would still be an adjective describing the shirt, but it would come after the noun it describes, not before

You also use hyphens to describe family relationships, such as brother-in-law, father-in-law, or mother-in-law. You use a hyphen when spelling out numbers. If you’re spelling out a number anywhere from 21 to 99, you need to spell it out and use a hyphen. Now once you get to a number above 99, such as 100, you still need to spell it out, but you don’t need a hyphen. From there, if you’re spelling out a number that would require you to use three words to spell it, you just write out the digits that make up the numbers, such as 102.

Here, we have two examples of the use of two thirds. “Only two thirds of the assembly were present.” “The proposition passed by a two-thirds majority.” You’ll probably notice that here no hyphen is used, and here a hyphen is used. In this case, “two-thirds” is an adjective. Remember, a compound adjective directly before the noun it describes needs to have a hyphen. This is a compound adjective directly before the noun it describes, so it needs to be hyphenated. Here, you may be thinking that “two thirds” is modifying “assembly”, but “assembly” is actually an object of a preposition. “Of” is the preposition and “assembly” is the object of the preposition. You could just take the prepositional phrase out of the sentence and it would read like this: “Only two thirds were present.” Here, it’s quite obvious that “two thirds” is the noun of the sentence. Since it is a noun, not an adjective, it does not need a hyphen.

Remember, earlier I said that you need to evaluate a compound on a case-by-case basis to determine if the use of a hyphen is necessary. This is a great example of that. Here, we have the same compound in both sentences, but, since they are used in different ways, one needs a hyphen and the other doesn’t. You also need hyphens when you have a compound that includes the word “self”. Now, there are some exceptions to this, such as “selfless”, which does not need a hyphen. When you use ex- or pro- before a word, you need a hyphen.

Whenever you are writing out a sentence and the last word of the sentence won’t quite make it on that line and you have to continue on the next line, it’s appropriate to break up the word. However, you need to break it up between syllables. “Giraffe”, for example, has two syllables, so you couldn’t just put a hyphen wherever you please, maybe after the “r” or the “a”. It has to be between the “i” and the “r”, because you can’t do a break in between a syllable. Now, if this doesn’t work for you and it won’t fit this way, then you can just leave an extra big space on that line and write the entire word on the next line.

Also, you use a hyphen to avoid confusion with the spelling of a word. Here you have the word “integral” and you want to add “semi” to it. If you didn’t have a hyphen here, the “i”s would be next to each other, which would create some confusion as to how to pronounce the word. By putting a hyphen, it really clears things up. There are some exceptions to this, such as “coordinate”. Most people don’t even think of “coordinate” as a compound, but really this can be written with a hyphen between the two “o”s, but now this word is so commonplace that a hyphen is no longer needed.



by Mometrix Test Preparation | Last Updated: February 19, 2019