Possible long barrow. This is contested by some, but asserted by others, who point to the lack of other similar natural features in the area. Claims are also bolstered by alleged traces of stone facing on the SW end of the mound, and the presence of rock art in the locale. Nearby flint scatters add a little bit more credence to these claims, though some of the flints have been attributed to the Mesolithic. I'm not sure of the dates for the cultivation terraces nearby, but they may have more to do with the IA hillfort.
A farmer I spoke to about it said that locals have always believed it to be a burial mound.
Unfortunately for me, I couldn't get an answer from the house to get permission to wander about their fields, so I gave closer examination a miss for the time being, and settled for peering through the trees from the nearest right of way.