Silver has a trace of tarnish? Horrified (6)
I believe the answer is:
aghast
'horrified' is the definition.
(I know that horrified can be written as aghast)
'silver has a trace of tarnish?' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'a trace of' suggests taking the first letters.
The initial letter of 'tarnish' is 't'.
'ag'+'has'+'t'='AGHAST'
(Other definitions for aghast that I've seen before include "Taken aback with horror" , "Stunned" , "Thunderstruck" , "Filled with consternation or horror" , "Amazed" .)