Hyphens ("-") connect two words to make a single word. Though they look similar to dashes ("–" and "—"), they serve a different purpose. The dash is a form of punctuation that comes in between words whereas hyphens combine words. Like most components of English punctuation, hyphens have general rules regarding how they should be used. Hyphens are often used to connect adverbs and adjectives when describing a noun. Let’s explore these concepts in greater detail. 

Linking Prefixes

Hyphens can be used to link prefixes such as non-, sub-, and super- to their main words. While it is possible (especially in American English) to attach these prefixes without hyphens, it is generally helpful to hyphenate when the letters brought into contact are the same. It's also helpful when the letters are vowels, when a word is uncommon, or when the word could easily be misread. For example:

• Non-negotiable
• Sub-basement
• Pre-industrial

Units

In general, values and units are hyphenated when the unit is given as a whole word:

• 30-year-old man
• One half-dose

Homographs

Homographs are words that are spelled the same, but mean different things and may be pronounced differently. To prevent confusion, hyphens can be used to distinguish between homographs. For example:

• Re-dress (to dress again)
• Redress (to remedy or set right)

Combining Adverbs and Adjectives 

Hyphens can be used to combine an adverb and adjective to describe a noun. In this situation, the adverb is describing the adjective, and the adjective is describing the noun. However, when the adverb ends with -ly, a hyphen should not be used. 

• Disease-causing nutrition
• Beautiful-looking flowers
• A well-meaning gesture

It is not always necessary to use a hyphenated word. Sentences can be rearranged to avoid the need for a hyphen. If the adverb and adjective come after the noun being described, a hyphen is not needed. For example:

• A light-blue handbag sat on the bench.
• The handbag was light blue.

Remember that using hyphens to combine adverbs and adjectives in this way creates a new word. The placement of hyphens can greatly change the meaning of a word, thus changing the entire sentence. Let’s look at some examples of how removing a hyphen changes the meaning. 

• Disease-causing poor nutrition. (Poor nutrition that causes disease.)
• Disease causing poor nutrition. (A disease that causes poor nutrition.)
• Little-celebrated paintings (Paintings that are underappreciated.)
• Little celebrated paintings (Small, appreciated paintings.)
• Government-monitoring program (A program that monitors the government.)
• Government monitoring program (A program the government monitors.)

Using hyphens correctly is important to clarifying these phrases.