A bicycle specially designed for off-road riding, typically with straight, flat handlebars, a heavier frame than road bikes, higher ground clearance, and wider tires, sometimes with knobs on them for greater traction.

(astronomy) the interval between the moon's successive passing of the same moving node.

The first full moon of autumn by a tropical year.

(physics) The motion of some hypothetical device that continues forever with no external input of energy, in violation of the laws of thermodynamics.

(physics, pseudoscience) A hypothetical device that exhibits perpetual motion, especially one that does useful work with no input of energy.

A belt concealed under clothing, having a pocket for money or other documents.

(firearms) a sight mount with a strong metal frame between the rings, used on large-caliber rifles to negate the effects of recoil on accuracy.

Government by violent gangs, or by the masses.

(geography) A series of adjoining mountains, often in a line.

The woman from whom one inherits half of one's DNA and who is the source of one's mitochondrial DNA.