Real Dictionary

lignite in American English
a usually soft, brownish-black coal in which the texture of the original wood can often still be seen: in the process of coalification it represents the intermediate stage in density and amount of carbon between peat and bituminous coal
noun: a soft coal, usually dark brown, often having a distinct woodlike texture, and intermediate in density and carbon content between peat and bituminous coal

lignite in British English
noun: a brown carbonaceous sedimentary rock with woody texture that consists of accumulated layers of partially decomposed vegetation: used as a fuel. Fixed carbon content: 46–60 per cent; calorific value: 1.28 × 107 to 1.93 × 107 J/kg (5500 to 8300 Btu/lb)