dolmen: [19] English acquired the word dolmen for a ‘prehistoric structure of two upright stones surmounted by a horizontal one’ from French, but its ultimate source is Celtic. The element men means ‘stone’ (it occurs also in menhir [19], literally ‘long stone’) but there is disagreement about the first syllable. It is usually said to represent tōl ‘table’, a Breton borrowing from Latin tabula ‘board, plank’, but another view is that it is Cornish tol ‘hole’, and that the compound as a whole means literally ‘stone hole’, a reference to the aperture formed by the top stone lying on the two side stones. => menhir
dolmen (n.)
1859, from French dolmin applied 1796 by French general and antiquarian Théophile Malo Corret de La Tour d'Auvergne (1743-1800), perhaps from Cornish tolmen "enormous stone slab set up on supporting points," such that a man may walk under it, literally "hole of stone," from Celtic men "stone."
Some suggest the first element may be Breton taol "table," a loan-word from Latin tabula "board, plank," but the Breton form of this compound would be taolvean. "There is reason to think that this [tolmen] is the word inexactly reproduced by Latour d'Auvergne as dolmin, and misapplied by him and succeeding French archaeologists to the cromlech" [OED]. See cromlech, which is properly an upright flat stone, often arranged as one of a circle.