A diagnosis is the identification of what's wrong when someone is sick or something isn't working properly. When you go to the doctor feeling ill, they ask questions, run tests, and examine you to figure out exactly what disease or condition you have. That conclusion is the diagnosis.

The word comes from doctors and medicine, where getting the right diagnosis matters enormously. If a doctor diagnoses strep throat instead of just a common cold, you'll get antibiotics that actually cure the infection. A wrong diagnosis means the wrong treatment, which is why doctors work so carefully to get it right.

The word has spread beyond medicine. A mechanic might diagnose why your family's car won't start, determining whether it's a dead battery or something else. A computer technician diagnoses software problems. Teachers sometimes diagnose learning difficulties to understand how to help a student succeed.

Diagnose is the verb form: “The veterinarian diagnosed our dog with an ear infection.” The plural is diagnoses (die-ag-NO-sees), so a doctor might review several diagnoses from different patients.

Getting an accurate diagnosis is often the first and most important step toward fixing a problem, whether that problem is medical, mechanical, or something else entirely.