Dynamo

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late 19th century: abbreviation of dynamo-electric machine, from Greek dunamis ‘power’.

wiktionary

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A shortening of dynamo-electric machine. The element dynamo- is ultimately from Ancient Greek δύναμις(dúnamis, “power”).

etymonline

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dynamo (n.)

"generator for converting mechanical rotation into electric power," 1882, short for dynamo-machine, from German dynamoelektrischemaschine "dynamo-electric machine," coined 1867 by its inventor, German electrical engineer Werner Siemans (1816-1892), from Greek dynamis "power," from dynasthai "to be able, to have power, be strong enough," which is of unknown origin.