enfermero
nurse
enfermo
sick
+
-ero
person who does something
Enfermero means nurse and can be thought of as a person who deals with1 (-ero1) those who are sick0 (enfermo0).
noun
  1. nurse
    A person trained to care for the sick or infirm, especially in a hospital
    El enfermero administró el medicamento al paciente. // The nurse administered the medication to the patient.