> (In reply to Mike Redmayne)
> you think so?
> so it's also inconsistent (and therefore wrong) to say:
> the truck has twin axles, but it's a twin-axled truck?
> the rifle's barrel had a small bore, but it was a small-bore rifle?
Yes, I think so, though I suspect we really need JCM to come tell us the rules!
Sea cliff is a compound noun, and Oxford says:
"In the past, these sorts of compounds were usually hyphenated, but the situation is different today. The tendency is now to write them as either one word or two separate words. However, the most important thing to note is that you should choose one style and stick to it within a piece of writing. Don’t refer to a playgroup in one paragraph and a play-group in another."
Or are you having 'sea' as an adjective?
Your other egs are different. Twin-axled I think is right, like small-minded. Small-bore is also right according to the OED (though I think you also find smallbore), but in that example you are moving from adjective plus noun (small bore) to adjective-noun compound.
Though looking at the online OED, I'm afraid they go for sea-cliff. Yikes. But the most recent source they quote for this is 1876, so I'm having sea cliff as the modern way (I'm sure Nicholson Baker, in his excellent essay on the history of punctuation, has it that some compounds lose their adjective as time goes by and people get used to the compound). Plus see the quote above. If you really want to do your head in, my concise OED has sea breeze and sea-breeze, with different meanings.
Anyway, looks as though the OP can do what he wants (though seacliff certainly looks wrong). Just be consistent.
People who obsess about this sort of thing often come across to me as small bores (no hyphen for sure?). Speaking as an ex-editor consistency is best but hey the world won't end if you miss the odd hyphen.
I am sure Ripper is correct. See your own link for an example of what you label inconsistency regarding the phrase 'well known'. When used predicatively there is no hyphen, but when attributively the hyphen is normal, and recommended by the OUP reference books. Though not, according to Hart's Rules, if the first word ends in 'ly': so 'poorly protected' would always be unhyphenated. That does appears to be an inconsistency, but it seems to be OUP practice.
In reply to coverdale: US-published books seem more willing to drop hyphens and run words together, but I'd think that sea-cliff would more common usage in the UK. Hypens eventually seem to get dropped in really common compound words but I've a feeling the dividing line is totally arbitrary.
I've just been reading 'Passage' by Connie Willis in a US edition on a Kindle and the copy editors obviously didn't worry about consistency: e.g., temporal lobe, temporal-lobe or temporallobe all occur.