A compound word consists of two or more base words. The meaning of the Compound words is often different from the separate base words.
Compound Words and Parts of Speech
Compound words are mostly nouns, adjectives, and verbs.
Kinds of Compound Words
Compound words are of three types:
(A). Closed Compound Words:
Words are joined together. There is no space or hyphen between the words.
Examples: firefly / softball / redhead / keyboard / makeup / notebook
(B). Hyphenated Compound Words:
Words are joined together by a hyphen.
Examples: daughter-in-law / over-the-counter / six-year-old
(C). Open Compound Words:
Words are not joined together. Words are open or separate. In other words, there is a space between the words.
Examples: post office / real estate / full moon / half sister
Some general rules regarding use of hyphens:-
Compound Adjectives are often hyphenated.
If compound adjective precedes a noun, they are hyphenated
Examples:
low-paying job [low- paying is a compound adjective; job is a noun]
easy-going celebrity [easy-going is a compound adjective; celebrity is a noun]
Adverbs that end in ly and compounded with another modifier are generally not hyphenated:
Examples:
deeply held beliefs
genetically modified foods
highly placed sources
quietly organized meeting
ALSO NOTE:
Some compound words may have more than one form but these forms may belong to different parts of speech.
fast track [open form] [noun]
fast-track [hyphenated form] [adjective, verb]
first degree [open form] [noun]
first-degree [hyphenated form] [adjective]
full time [open form] [noun]
full-time [hyphenated form] [adjective, adverb]
gift wrap [open form] [noun]
gift-wrap [hyphenated form] [verb]
hard core [open form] [noun]
hard-core [hyphenated form] [adjective]
hard line [open form] [noun]
hard-line [hyphenated form] [adjective]
road test [open form] [noun]
road-test [hyphenated form] [verb]
second hand [open form] [noun]
second-home [hyphenated form] [adjective]
Some compound words which are hyphenated in American English are not hyphenated in British English.
Example: cash-back [American English]; cashback [British English]