Calculus vexes tenor (9)
I believe the answer is:
gallstone
'calculus' is the definition.
(gallstone is a kind of calculus)
'vexes tenor' is the wordplay.
'vexes' becomes 'galls' (I've seen this in another clue).
'tenor' becomes 'tone' (synonyms).
'galls'+'tone'='GALLSTONE'
(Other definitions for gallstone that I've seen before include "Concretion of cholesterol, lime salts, etc" , "Problem for bile ducts" , "Small hard secretion formed in the body" , "It's removed in hospital" , "Let Anglos suffer with small hard mass in body" .)