Hyphens and dashes

Q. What is a hyphen?
A. Hyphens are used to divide or to compound words, word elements, or numbers

Q. When do I use a hyphen to combine two words?
A. Use a hyphen to combine two words when modifying a noun

• This three-inch heel = GOOD
  
• This heel is three-inches = BAD
  
• Infuse your wardrobe with urban-chic… = BAD
  
• This urban-chic offering…  GOOD

EXCEPTION: adverbs ending in ly NEVER get a hyphen

• Beautifully-crafted leather = BAD

Q. Do I use a hyphen before a prefix?
A. Generally not, although the rule varies from word to word. When in doubt, visit m-w.com and look up the prefix (pre-, under-, etc.). Often you can find the correct usage of the word you are looking for in the word list under the prefix entry

Q. What’s the difference between a hyphen and a dash?
A. There are three types of dashes:

• Hyphen (or i-dash): looks like - and is used to compound words as above
  
• En-dash: looks like – and is used when omitting entries between two items, such as dates or amounts (1997–1998)
• Em-dash (or double hyphen): looks like — and is used to interject information in a sentence. (A lot of people don’t know the differences between dashes—can you believe that?)

Final fact: One never uses spaces on either sides of a dash.