It can be compared to a derivative, which is made up of a word plus a bound structure such as a prefix or a suffix.
Example
Backache and filmgoer are examples of compound words.
In the classroom
Compound words are an excellent way to help learners expand their vocabulary, for example by focusing on one head word - such as ache in the example above - and then looking at what modifiers can go with it. Learners sometimes need help with the question of whether compounds are together, separate or hyphenated, and can be encouraged to use dictionaries to check this information.