5 Pairs Of Compound Words, And How They’re Compounded

A while back, I wrote about compound words involving front and back, in and out, and up and down, and the bewildering variety of styles (open, hyphenated, and closed) for each group. Here are five more pairs of words to watch for when they're used in compound phrases.

1. Light and Dark

To be light-headed and to be lighthearted are not strictly analogous — one is a physical sensation, and the other refers to an emotion (though it may result in a physical response) — but they are both adjectives. So, why is one (and similar compounds like light-fingered and light-footed) hyphenated and the other closed? I confess I'm in the dark. But note that compounds beginning with dark are always open ("dark days" "dark horse," "dark matter").

Most other noun compounds beginning with light ("light meter," "light pen") are open, but notice light-rail, which, like a few other compound nouns (mind-set, life-form), remain stubbornly hyphenated (though the meaning of light here differs; it's akin to the definition in the previous paragraph). When the noun light is the last element of a compound, it's always closed: candlelight, flashlight, searchlight.

2. Mind and Brain

I'm going to go out of my mind. Why is one simpleminded yet single-minded? Is it because one is a presumably perpetual state that a person so designated has little or no control over, while the other is a personality trait? But compounds beginning rather than ending with mind generally obey these rules: open in noun compounds (with the previously noted exception of mind-set and the obscure mind-healer, as well as the jargony mindshare) and hyphenated in adjectival compounds such as mind-bending and mind-boggling).

Brain, meanwhile, is almost always open ("brain trust," "brain wave"); brain-dead is a rare exception.

3. Right and Wrong

Compounds employing these words for practical or moral choices are generally open ("right angle," "wrong side"), but phrasal adjectives with prepositions (right-of-way, right-to-work) are always hyphenated.

4. Right and Left

Most compounds employing right or left as directions are open (noun phrases like "left wing," adverbial phrases such as "right away"), but the phrasal adjectives left-handed and right-handed (also adverbs) are always hyphenated.

5. Smart and Dumb

By now, you know not to expect logic in idiomatic phrases — it's "smart aleck" but smart-ass (or smart-mouth). Open phrasing, however, is preponderant for smart and dumb: "smart card," "smart drug," "dumb down," "dumb show" (pantomime). Street-smart is hyphenated, but "street smarts" is open.

Thanks to Mark Nichol / Daily Writing Tips
http://www.dailywritingtips.com/5-pairs-of-compound-words-and-how-they%E2%80%99re-compounded/