Compound verbs may be either hyphenated or written solid. The only safe rule is to check your dictionary:
- freeze-dry
- mass-produce
- age-harden
- spoon-feed
- bad-mouth
- extra-bill
but
- waterproof
- downgrade
- sidetrack
- proofread
If the infinitive form of the verb (e.g. to air-condition) is hyphenated, retain the hyphen in all other forms, except in the case of certain gerunds (see below):
- The theatre was air-conditioned.
- You need an air-conditioning expert.
Gerunds
Hyphenate gerunds formed from hyphenated compound verbs only if they are followed by a noun object:
- Dry cleaning is the simplest way to clean a sweater.
but
- Dry-cleaning the sweater should remove the stain.
- Air conditioning is sometimes needed in summer.
but
- Is air-conditioning the building feasible?
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