Hyphens are used internally in some compound words to separate the words forming the compound word.
Examples: merry-go-round editor-in-chief
When unsure of the hyphenation of such words, check a dictionary. Usage may vary. As some words are more widely used, the hyphen is dropped. For example, in the early 1800s the word blackbird was usually spelled black-bird. Now the hyphen has been dropped.
Hyphens connect the words of a compound modifier that comes before the word being modified. Hyphens are not used this way with compound parts ending in -ly or made up of proper nouns or proper adjectives.
Incorrect: He is a well respected man.
Correct: He is a well-respected man.
(A compound modifier before the noun.)
Incorrect: That man is well-respected.
Correct: That man is well respected.
(The modifier follows the noun, no hyphen.)
Incorrect: That was a badly-punctuated sentence.
Correct: That was a badly punctuated sentence.
(Modifier ends in -ly, no hyphen.)
Incorrect: The South-American rain forest is home to hundreds of species of hummingbirds.
Correct: The South American rain forest is home to hundreds of species of hummingbirds.
(Modifier is proper, no hyphen.)
Some authorities recognize the use of a hyphenated compound adjective following the verb to be, especially if necessary for clarity.