In the 1771 edition of the Encyclopaedia Britannica, exponent is spelled differently (in the Logarithm article): "Dr. Halley, in the philosophical transactions, ... says, they are the exponements of the ratios of unity to numbers" [James A. Landau].EXPONENTIAL...
1797 in Nicholson’s Journal where it is spelled "gramme." Kilogram and liter are found in English in Aug. 1797 in Journal of Natural Philosophy. Kilometer, milliliter, millimeter, and milligram are found in English in Noah Webster’s 1806 A Compendious Dictionary of the English Language, ...