There are a number of ways of diagnosing disease: tissue biopsy, symptom matching, and of course, clinical signs. People often use the latter two terms interchangeably, especially since they are often paired together via the phrase “signs and symptoms.” But rigorously, these two words refer to two different things. Perhaps their etymologies will help differentiate them:

Sign
Origin: Latin, signum (sign/image)
Something the clinician notes in during a clinical encounter

Symptom
Origin: Greek, sym- (together) + piptein (to fall)
Something a patient reports to the clinician; something that “falls together” with something else

In other words, symptoms are subjective experiences while signs are objective experiences. For example, if I tell my doctor I have a fever, that is considered a symptom, but if he or she were to measure my temperature and find it elevated, it would be a sign. Another good example: pain is a symptom, since the perception of pain is unique to each patient. Tenderness, however, is a sign, since it is elicited by a clinician, e.g., applying pressure to the abdomen and eliciting an “ouch!”

St. Francis Receives the Stigmata, by Antoni Viladomat (1678-1755)

There is another pair of terms that are often used together that is also often conflated. These words are stigma (plural stigmata) and sequela (plural sequelae). A stigma is a readily-visible (cutaneous or otherwise) or discernable sign that is characteristic of some disease. A classic stigma of liver disease is jaundice.A sequela, on the other hand, is an abnormal state or complication that results from a previous disease. A classic sequela of diabetes is diabetic nephrophaty. The etymologies of these words are relatively straight-forward:

Stigma
Origin: Greek, stizein (to mark/tattoo)

Sequela
Origin: Latin, sequi (I follow)

Interestingly enough, the word “stigmata” is also used in theology to refer to the bodily marks or sensations of pain associated with the crucifixion [Origin: Latin, crux (cross) + figere (to fix/bind)] of Jesus. Those who bear these stigmata are called “stigmatics” or “stigmatists,” and a common motif in classical painting is St. Francis of Assisi’s reception of the stigmata (see above). St. Francis supposedly received the stigmata of Christ for his great piety during the Feast of the Exaltation of the Cross after a forty-day fast.

Regarding jaundice, a stigma of liver disease, we know it to be the yellowing of the skin due to increased levels of bilirubin. Jaundice can, of course, be caused by a number of other conditions, e.g., deficiencies in certain enzymes (cf. Gilbert syndrome). There is one part of the body that is not said to be jaundiced when yellow; that honour falls on the eyes. When the eyes turn yellow due to, say, liver disease, we call it scleral icterus.

Jaundice
Origin: Latin, galbinus (yellow/yellow-green)

Icterus
Origin: Greek, ikteros
A bird said to cure jaundice when spotted

Hence we call it scleral icterus because it is with our eyes that we see the ikteros and become cured of our jaundice!