Compound Nouns – Written Separately or Together?

Should you write the words as one word or two? That is the question!  There are not hard, fast rules.  Why is that?

Historically, compound nouns that have established themselves in the spoken language are written as two words.  As time goes by, they’re separated with a hyphen, and finally, they’re written as one word.

  1. make up          2. make-up               3. makeup

For example, it’s acceptable to write the word makeup with and without a hyphen.

The reason for the differences are therefore based in the etymology of the word and how established its usage is.  It’s not easy to determine how old a word is, either!  You’d think, for example, that the word notebook is relatively new. Actually, the word is from c. 1570.  The word hotspot is also older than you think!

It’s best to use a good dictionary, because it’s near impossible to know how established a word is in the English language. By the way, the hyphen is used more for British English than it is for American English.


For computer users:  

PC words are writen as one word, or they’re separated with a hyphen.

file name filename                        home page homepage


For biology students:

English dictionaries write insect names as one word:

honeybee, bumblebee

Scientists[1] write insect names as two separate words. Why is that? Entomolygists use two words, because they need the first word to identify what class of bug it is.  In the example, these are two kinds of bees with different characteristics:

honey bee, bumble bee,

Butterfly, firefly and dragonfly aren’t really flies.  A ladybird isn’t really a bird.  That’s why these words are not written as two words. They’re words that have derived from the common language. Entomologists have their own names for these insects.

That brings us to an interesting point: Journalists and non-scientists use regular dictionaries. If you’re studying a profession, use the appropriate databases and scientific journals as your sources.  If you’re a injection molding specialist, do you write hot-runner or hotrunner in your paper that is to be published?  This is where the Merriam-Webster, Oxford, and Cambridge dictionaries fall short! 😊


What are the forms?

  1. Nouns + Adjective

New words that are made up of a noun and an adjective are often separated by a hyphen

  • part-time, fast-food, tax-free,

Words that have the following endings are written without a hyphen:

  • -proof, -wide, -sick, -long

Examples:  soundproof, worldwide, homesick, lifelong

  1. Noun + Preposition

Words that have the following endings are written without a hyphen

  • -out, -down, -up, -over, -off, -about

Examples:  blackout, burnout, sundown, lineup, leftover, kickoff, roundabout

  1. Noun + Noun

bookstore, bathroom, fishbowl, newspaper


  1. Noun + Verb

homework,  waterfall, headache


Words that have the following nouns as head words are now being written as one word:

  • hand-, block-, pain-, home-, heart-

handshake, homebase, painkiller, heartbreak, blockbuster


Words starting with head- are still written as two separate words, but more and more are being written as one word:

  • headache, headmaster, headstrong BUT   head start, head count


  1. Verb + Noun:

 popcorn, chopstick, checklist, driveway


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