This is the 620th most frequent Spanish word.
médico
Doctor.
In this sentence, 'médico' is used as a noun referring to a person who practices medicine.
El médico revisó a sus pacientes en la clínica.
The doctor examined his patients in the clinic.
Here, 'médico' is used as an adjective describing the book as being related to the field of medicine.
Compré un libro médico sobre anatomía humana.
I bought a medical book about human anatomy.
In this context, 'médicos' is used as an adjective in plural form relating to advancements in the medical field.