pathognomonic
Concise Oxford English Dictionary © 2008 Oxford University Press:
pathognomonic /ˌpaθəgnə(ʊ)ˈmɒnɪk/
▶adjective Medicine indicative of a particular disease or condition.
– origin C17: from Gk pathognōmonikos ‘skilled in diagnosis’, from pathos ‘suffering’ + gnōmōn ‘judge’.
'pathognomonic' also found in these Oxford entries:

