My 3rd edition of Fowler's Modern English Usage has a lot to say on the subject of hyphens, but it lacks the honest admission of the 2nd edition that resides on JD's desk: "No attempt will be made here to describe modern English usage in the matter of hyphens; its infinite variety defies description."
Both editions offer pages of advice on hyphens, but this is an area where usage is constantly changing. Reflecting this, the latest (6th) edition of the Shorter Oxford English Dictionary has dumped no less then 16,000 hyphens, many of them from compound nouns. Traditionally, paired words start separate, gain a hyphen and finally merge. An example close to my heart is motorised bicycle which became motor bicycle, motor cycle, motor-cycle and finally motorcycle.
But in many cases those nice people at Oxford have reversed the traditional process by reverting from a hyphenated pair of words to two separate words. Thus fig-leaf becomes fig leaf; other separated pairs include hobby horse, ice cream, pin money, pot belly and test tube.
Following the more usual process by squeezing out the hyphen to become a single word are bumblebee, chickpea, crybaby, leapfrog and logjam (though I can't say I like the look of the gj at the centre of logjam).
As far as I know we Brits still like a hyphen in the middle of our port-holes as an aid to pronunciation, while our American cousins are quite happy with porthole. Clarity, as always, is the name of the game.
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