Tensions over the concept, called "decarbonisation", illustrate how wide the divides remain less than six weeks before a 195-nation UN forum gathers in Paris to try to tame climate-altering forces.
Their overarching goal is to limit global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels so as to avoid dangerous consequences such as rising sea levels, increasingly violent storms, large-scale droughts and spreading disease.
Two decades of negotiations over how to rein in global warming have been fraught with disagreements.
Just weeks ahead of the November 30-December 11 meeting in Paris, nations cannot even agree on the meaning of decarbonisation -- does it denote a desired outcome, or an open-ended odyssey? Does it apply only to CO2 or other greenhouse gases too?
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The term has flashed in and out of various versions of a draft agreement to be presented to ministers and heads of state in the French capital.
"It tells us the direction of travel, and where we want to be by 2050, by the end of the century, and how we are going to get there," said climate activist Mohamed Adow of Christian Aid, a group fighting for the rights of poor countries.
Unlike many issues bedevilling the talks, the tussle over decarbonisation does not respect the traditional split between rich and developing nations.
The European Union -- aligned with Washington on most climate matters -- resists using the word.
This is despite French President Francois Hollande and German Chancellor Angela Merkel successfully lobbying other members of the Group of Seven (G7) rich nations to enshrine decarbonisation in a joint statement in June.