enfermo
/enˈfeɾmo/ · A2 · adj
sick, ill
🤒 en-FERMO = in + firm: Latin infirmus, not firm, like English infirm
From Latin infirmus (in- not + firmus strong). English kept it as infirm and infirmary, the place for the sick. Spanish shifted in- to en- and the i to e: infirm -> enfermo. Someone enfermo is literally not firm.