Hyphen With Noun, Adjective Or Adverb And Present Participle
When using a noun, adjective or adverb and a present participle (a word ending in ‑ing), we often have to put a hyphen between the two words to make it clear as to which word is modifying which.
There are some beautiful looking flowers in the garden.
Without the hyphen between beautiful and looking, we’re not sure if looking is modifying beautiful or flowers (perhaps it’s a new type of flower?).
There are some beautiful-looking flowers in the garden.
Fast-acting medication can be useful when one has a headache.
N.B. This rule only applies if the adjectives come before the noun. If the adjectives come after the noun, you don’t need to hyphenate them.
The medication is fast acting.
There is some disagreement as to whether or not an adverb needs to be hyphenated, especially if the adverb ends in ‑ly. In British English, the hyphen is consistently used, but it’s usually left out in American English (unless it’s needed for clarity).
The room was like a heavily decorated chocolate box.
Because the adverb heavily is clearly modifying the verb decorated, no hyphen is required in this sentence.