Former European Currency Unit, a precursor to the Euro, or an Engine Control Unit in automotive contexts.
For the currency, from French écu, an old coin name from Latin scutum 'shield.' For automotive, it's an acronym for Engine Control Unit, developed in the 1970s as cars became computerized.
The ECU currency was cleverly named after the historical French coin to give the new European unit a sense of monetary tradition. Meanwhile, your car's ECU is basically its brain, controlling everything from fuel injection to emissions!
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