Sorry, hadn't seen this question before. The term comes from the Breton / Welsh / Cornish language, from the words crom and lech, meaning something like crooked and stone slab.
In France, a cromlech is a stone circle, or a ring of stones. Or sometimes a sort of stone enclosure, which can often be horseshoe shaped. In Welsh, a cromlech usually means a dolmen (dol and men = table and stone).
I have no idea why the meaning is different in the two places, after all it comes from the same root. And I am sure others can explain much better than me the intricacies of the language of which I know very little.
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