methane

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An odorless, colorless, flammable gas, CH₄, the major constituent of natural gas, that is used as a fuel and is an important source of hydrogen and a wide variety of organic compounds.

from The Century Dictionary.

• noun A hydrocarbon (CH₄) belonging to the paraffin series, a colorless, odorless gas which may be reduced to a liquid by extreme pressure and cold.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) A light, colorless, gaseous, inflammable hydrocarbon, CH4; marsh gas. It is the simplest of the aliphatic hydrocarbons. See Marsh gas, under gas.
• noun (Chem.) a series of saturated hydrocarbons, of which methane is the first member and type, and (because of their general chemical inertness and indifference) called also the paraffin (little affinity) series. The lightest members are gases, as methane, ethane; intermediate members are liquids, as hexane, heptane, etc. (found in benzine, kerosene, etc.); while the highest members are white, waxy, or fatty solids, as paraffin proper.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry, uncountable The simplest aliphatic hydrocarbon, CH4, being a constituent of natural gas.
• noun organic chemistry, countable Any of very many derivatives of methane.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a colorless odorless gas used as a fuel