the branch of medical science dealing with the classification of disease
"The hospital established a new department dedicated to diagnostics, focusing on the precise classification and identification of various diseases."
plural of diagnostic
"The technician ran diagnostics on the engine to determine if it was still capable of performing its intended functions."
The process of determining the state of or capability of a component to perform its function(s)
In plain English: Diagnostics are tests used to find out what is wrong with something so it can be fixed.
"The doctor ran several diagnostics to find out what was wrong with my chest pain."
Usage: Use diagnostics when referring to the systematic testing and analysis performed by computers, medical professionals, or mechanics to identify faults. This term specifically denotes the active investigation required to determine why a system is malfunctioning rather than just observing that it has failed.
The word comes from the Latin diagnosticus, meaning capable of distinguishing or identifying a disease. It entered English as an agent noun derived from the verb to diagnose before taking on its current plural form referring to medical tests and procedures.