Definition of "beetling"

As I anticipated, we had passed right through the precipice, and were now on the farther side, and immediately beneath its beetling face.

1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887

The beetling head of the cliff projected over the cane-brake.

1912, Arthur Conan Doyle, The Lost World […], London, New York, N.Y.: Hodder and Stoughton

Put a clay pipe in [Richard] Nixon’s mouth and a hod on his shoulder or a shillelagh in his hand, and there, complete with beetling brows and uptilted nose, is the original of the old cartoon stereotype of the fighting Irishman—the Irishman of the draft riots or of Punch’s version of the Sinn Feiner.

1960, Stewart Alsop, “How They Got that Way: Nixon”, in Nixon & Rockefeller: A Double Portrait, Garden City, N.Y.: Doubleday & Company, page 124

If the fire, with its giant black kettle swung over the flames, is our never-extinguished shrine, then the stove is an altar. It is habitually tended by my step-aunt Calliope (usually known as Calli), a dark, stocky, dense-looking woman with beetling black brows and a tied-back sheaf of thick hair, still raven-black without a trace of silver after her forty-four years.

1995, Iain Banks, Whit