I always thought electronvolt was an unit of energy and I knew its definition, but in these days I got some doubts because I saw 2 times it was used as an unit of mass: in my school textbook, in an article about the 4 fundamental forces, it was used as a mass unit; and in a famous magazine I read the same thing (same arguments)

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> In physics, the electron volt (symbol eV; also written electronvolt[1][2]) is a unit of energy equal to...
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particularly there was a table about sub-atomic particles with .... spin | charge | **mass(GeV)** | ...