A compound adjective, sometimes also known as hyphenated adjective, is an adjective formed by two or three words, none of which are necessarily adjectives themselves, but which used together make a very flexible way of describing things, people, etc.
One typical use is to combine a number with a noun (don't forget that the noun, now forming part of the adjective, must be singular), so a camera that costs 300 euros = a 300-euro camera.
Though compound adjectives are usually hyphentated, there are several exceptions: downhearted; downhill; fed up; homesick; lovesick; underpaid, etc.
Collocations are a very useful way of learning compound adjectives.
- Adjective or adverb + past participle: double-barrelled; left-handed; low-paid; old-fashioned; quick-witted;
- Adjective or adverb or noun + present participle: easy-going; good-looking; hard-working;
- Noun + past participle: tongue-tied; spin-dried; spoon-fed;
- Noun + adjective: duty-free; knee-high; lead-free; long-range; smoke-free; world-famous;
- Adjective + noun: full-length; high-rise; last-minute; short-term;
- Number + noun: a ten-page booklet; the four-minute mile.