Fermi, for one

The crossword clue “Fermi, for one is UNIT” is asking for a three-letter word that refers to the type of measurement unit that Italian physicist Enrico Fermi is associated with. The answer to this clue is “eV” (electron volt), which is a unit of energy commonly used in atomic and nuclear physics. Enrico Fermi was a Nobel Prize-winning physicist who made significant contributions to the development of nuclear energy and the study of subatomic particles. The clue is hinting at the fact that Fermi is often mentioned in the context of measurements and calculations involving eV.