Dental deposit (6)
'dental deposit' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tartar that I've seen before include "She terrifies" , "Fearsome person: kind of sauce" , "Cold sauce, popular with fish" , "Deposit that forms on teeth" , "Hard, crusty deposit on the teeth" .)
(Other definitions for plaque that I've seen before include "Memorial slab" , "Brass memorial tablet" , "Dental deposit" , "Commemorative tablet - unwanted film on teeth" , "Sticky deposit on teeth" .)