noun.
A combustible gas, chiefly methane, occurring naturally in mines from the decomposition of coal.
noun.
The explosive mixture of firedamp and air.
The Century Dictionary and Cyclopedia
noun.
The gas contained in coal, often given off by it in large quantities, and exploding, on ignition, when mixed with atmospheric air.
the GNU version of the Collaborative International Dictionary of English
noun.
a mixture of gases (mostly methane) that forms in coal mines and becomes explosive when mixed with air. It is a source of serious hazard in coal mining operations.