When should a hyphen be used in a compound word?

A hyphen should be used in a compound word in the following situations:

1. To join two or more words that together form a single adjective before a noun. For example, "well-known author," "high-quality product," or "state-of-the-art technology."

2. To avoid confusion or ambiguity. Hyphens can be used to clarify the meaning of a word or phrase. For instance, "re-cover" (to cover again) versus "recover" (to regain health or strength), or "re-sign" (to sign again) versus "resign" (to quit or give up).

3. To connect a prefix or suffix to a word. Hyphens are used to attach certain prefixes or suffixes to a base word, such as "pre-approval," "self-esteem," or "child-friendly."

4. To indicate a compound number. When writing numbers from twenty-one to ninety-nine, a hyphen is used to connect the tens and units place, such as "thirty-five" or "eighty-nine."

5. In certain compound nouns or adjectives. Some compound words require a hyphen to maintain clarity or to avoid confusion. Examples include "mother-in-law," "well-being," or "up-to-date."

It is important to note that not all compound words require a hyphen. Many compound words are written as one word without a hyphen, such as "football," "notebook," or "sunflower." The use of a hyphen depends on the specific word and its usage in a sentence.