pathognomonic (adj.)

before vowels path-, word-forming element in science and technical terms meaning "suffering, disease," from Greek pathos "suffering, disease" (from PIE root *kwent(h)- "to suffer").

"vertical shaft that tells time by the shadow it casts" (especially the triangular plate on a sundial), 1540s, from Latin gnomon, from Greek gnōmōn "indicator (of a sundial), carpenter's rule," also, in plural, "the teeth that mark the age of a horse or mule," literally "one that discerns or examines, interpreter, expert," from gignōskein "to come to know," from PIE root *gno- "to know." In geometry from 1560s, from a use in Greek. In early use in English sometimes folk-etymologized as knowman. Related: Gnomonic.

Proto-Indo-European root meaning "to suffer."

It forms all or part of: anthropopathy; antipathy; apathy; empathy; idiopathy; nepenthe; osteopathy; -path; pathetic; -pathic; patho-; pathogenic; pathognomonic; pathology; pathos; -pathy; psychopathic; sympathy.

It is the hypothetical source of/evidence for its existence is provided by: Greek pathos "suffering, feeling, emotion, calamity," penthos "grief, sorrow;" Old Irish cessaim "I suffer;" Lithuanian kenčiu, kentėti "to suffer," pakanta "patience."