What does the cryptic crossword clue "Shocked at gash that looks nasty (6)" mean?

The definition is "Shocked". The wordplay uses an anagram. anagram of AT + GASH = AGHAST; definition: "Shocked" The answer is AGHAST.

Shocked at gash that looks nasty (6)

Independent Cryptic #11047 | 8 Down | 2022-03-10 flower