diagnostic

Short definition from Wiktionary

Adjective

1. 1
   Of, or relating to diagnosis.
2. 2
   Characteristic of a particular disease.
3. 3
   Serving to indicate or specify a particular item or thing within a group of similar things.
4. 4
   Intended to assess a student's preexisting knowledge on the material being taught.
5. 5
   (of a skeletal or genetic feature) Characteristic of a particular taxon or clade.

Noun

1. 1
   Any technique used in medical diagnosis.
2. 2
   Any tool or technique used to find the root of a problem.
3. 3
   That by which anything is known; a symptom.