'tartar-forming' is a compound of 'tartar' and 'forming'. 'tartar' originates from French 'tartre', via Medieval Latin 'tartarum' and ultimately from Greek 'tartaron', where the root referred to salts or residues left by fermentation; 'forming' comes from Latin 'formare' (to shape) via Old French and Middle English.

'tartar' changed from Medieval Latin 'tartarum' and entered English as 'tartar'; 'form' (from Latin 'formare') passed through Old French and Middle English into modern English, producing the participial form 'forming' and the compound 'tartar-forming'.

Initially, 'tartar' referred more generally to a crusty residue or salts (e.g., from fermentation); over time, in medical/dental usage it became specialized to mean the hard dental deposit now called 'tartar' (dental calculus). 'forming' has remained with the sense 'causing to take shape' or 'producing'.