English (like many other world languages) contains a subset of vocabulary words that are classified as compound words – that is, two or more other words are put together (or “compounded”) to make one new word. This new word may or may not have a meaning that relates to one or both of the original words. Here are some examples of compound words: blackboard, redneck, undercut, sleepwalk, basketball, wallpaper, lawsuit, armchair. In this list, you can see words that relate directly back to the original words (a basketball is a ball you toss into a basket – at least according to the original game) and ones that end up having a different meaning (redneck is a term for a person who generally holds provincial and/or bigoted beliefs, not someone with a red-colored neck). In general, most words are fairly easy to understand based on the definitions of the original words.

Sometimes the original words have one meaning when they’re separate, and another meaning when compounded. For example, the phrases “I got sunburned and now I have a red neck” and “His redneck uncle really hates the current immigration policy” express two entirely different concepts. This can be confusing to many people, so it’s important to know when to use each form. We’ve picked five of the most commonly-confused compound words, and given examples below of how to use them correctly.

everyday vs. every day
Everyday is an adjective that means “commonplace, ordinary, routine” but the phrase every day refers specifically to time-based actions or occurrences.
Example: Every day this week I’ve had to go through the everyday correspondence of all of the company employees, looking for evidence of work-related fraud.

all together vs. altogether
The adjective altogether means “completely, totally.”
Example: The taste of the three herbs is altogether different when they are eaten all together rather than separately.

every one vs. everyone
Everyone is a pronoun referring to a group of people as a whole; every one refers to individuals considered separately.
Example: Everyone knows the quote from Dickens’ “A Christmas Carol” where Tiny Tim says, “God bless us, every one!”

back up vs. backup
You undoubtedly do computer backup (a noun), but you can also back up (a verb) your computer.
Example: She’ll back up my statement that the project won’t succeed without adequate technical backup from the IT department.

work out vs. workout
Keep an eye out for word pairs like this that are verbs when separate, but nouns when compounded.
Example: If we can work out the differences in our schedules, we should be able to plan a 30-minute workout session together at least twice a week.

Learn when to keep words together, and your English vocabulary skills will set you apart from the crowd.