Compound words are made when two or more words join (with or without a hyphen) to form a new word and subsequently, a new meaning. Common English words are frequently combined to form compounds. Compound words exist in many languages and offer great insight into the inner workings of each language including the basic building blocks such as suffixes, prefixes and word roots.
There are three different types of compound words: the closed form in which two words are joined together to create a new meaning such as redhead, notebook etc., the hyphenated form in which the words are joined together by a hyphen such as daughter-in-law, six-year-old etc. and the open form in which the words are not joined but when read together, they form a new meaning such as post office, real estate etc.
Many different parts of speech such as nouns, verbs, adverbs and adjectives combine together to form compound words. We have different types of compound words such as noun-noun compounds like fireman, classroom etc., verb-noun compounds like spoilsport, pickpocket etc. ,verb- adverb compounds like drop-out, fall-out etc., adjective-noun compounds such as hardware, software etc., and so on.