British English (and the SI standard) uses the spelling "tonne" to mean 1000kg, with "ton" meaning one of the obsolete units. American English prefers "metric

British English (and the SI standard) uses the spelling "tonne" to mean 1000kg, with "ton" meaning one of the obsolete units. American English prefers "metric ton", but they haven't obsoleted the old units. The ESA uses "tonne": https://www.esa.int/Safety_Security/Space_Debris/Space_debris_by_the_numbers https://www.esa.int/Safety_Security/Space_Debris/Space_debri... A "tun" is a type of barrel (Latin: tunna, German "Tonne"). One could contain roughly a tonne of liquid.