A melakol was a Romulan unit of pressure.

Aboard a Romulan science vessel in 2368, Mirok reported that pressure in the ship's containment chamber had increased fifteen melakols in two minutes. Soon after, the pressure had increased by two hundred melakols. This resulted in the Romulan crew losing control of the containment chamber, and necessitated the ejection of the entire engine core. (TNG: "The Next Phase")