Something to commemorate a cause of tooth decay (6)
I believe the answer is:
plaque
'decay' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for plaque that I've seen before include "Dental coating" , "Brass memorial tablet" , "Build-up on teeth" , "Film on teeth that encourages caries" , "Memorial slab" .)