Some English teachers try to teach rules about when to hyphenate words and when not to. The problem is that English has no firm rules and each example is judged on its own. One of the attempts to create a rule is the walking stick rule.
A walking stick is a stick that walks, and the phrase might occur as a metaphorical description of a stiffly behaved person; a walking-stick or walkingstick is a stick for walking.
Fowler (1908) The King's English
The rule does not match English as the language is used. According to this rule a two-word compound does the action itself; whereas a one-word compound is used to do the action.
‧Children colour pictures in colouring books. Colouring books are not books that do their own colouring.
‧Dining rooms are rooms for dining (eating dinner). The room does not do the eating.
‧A post office is an office for posting things. The office itself is not posted. (or does the posting)
This fun colouring book is packed full of cute and cuddly Precious Planet animals for little ones to colour.
Our residents share dining facilities with Starr Hall in the adjoining multi-purpose dining room, Ho Tim Hall.
Hongkong Post announced that the Hennessy Road Post Office will be closed down.
Sometimes the so-called rule does fit, but not often enough to accept this as a rule.
A walking floor is a type of conveyor belt running down the centre of the floor of a truck to help unload the cargo. It is a floor that walks!
Fowler's walking stick is also the (US English) name for a stick insect. It is a stick-like insect that walks.
Scientific names are usually not hyphenated, except for those in very specific naming systems.
Coriandrum sativum (It is the scientific name for the plant we call coriander.)
Carbon dioxide (A chemical compound)
(3β)-cholest-5-en-3-ol (It is a precise chemical name for cholesterol.)
As a general pattern words that don't make sense on their own are merged into one.
Examples: Silverfish, honey bee...
A silverfish is a gray insect found in Hong Kong, that damages books. It is not a fish and is not made of silver. To write silver fish is misleading, silverfish is easier to understand.
A honey bee makes the honey we eat. It makes sense as separate words. However it is more common to write honeybee, which has a frequency rating of 185, than to write honey bee which is slightly less frequent at 166. The hyphenated version honey-bee only gets a frequency rating of 4. (Frequency rates in the article are according to COCA, the Corpus of Contemporary American English)
Airconditioner, air conditioner and air-conditioner are all correct. However it is better to use the most common form. The relative rates of use are airconditioner, 5; air conditioner, 788 and air-conditioner, 178. So it is suggested that air conditioner is the preferred form.
Even if English uses more than one form, you should not. Consistency is more important than your choice of form. Readers will recognize each version. If they see multiple versions on one page it will look messy. (Unless of course you are writing about the different forms.) Usually it is better to avoid hyphens. Names are usually not hyphenated, unless the person named prefers to write it that way. Hyphens are best used when your writing appears clearer with them.
Next week I will cover a special type of hyphenated word, words with hyphenated prefixes.