Crossword Genius

See sign showing decay (6)

Ross

I believe the answer is:

caries

'decay' is the definition.
(dental caries)

'see sign' is the wordplay.
'see' becomes 'c' (the word for the letter, according to Chambers).
'sign' becomes 'Aries' (star sign).
'c'+'aries'='CARIES'

'showing' is the link.

(Other definitions for caries that I've seen before include "I scare easily with tooth decay" , "Decay in bones or teeth (6)" , "Dental decay" , "Decayed area in a tooth" , "Decay of bone or teeth" .)

I've seen this clue in The Guardian.
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