IPA: /ˈɡrɪzli/
KK: /ˈgrɪzli/
Causing a strong feeling of fear or disgust; very frightening or horrible.
The grisly scene in the movie made many viewers feel uneasy.
Grisly originates from Old English 'grislic', meaning fearful or horrible. The word is formed from 'gris' (meaning fear) and the suffix '-ly' (meaning in a manner of). Thus, grisly describes something that is fearfully horrible or gruesome.
Think of something that inspires 'fear' ('gris') and is described 'in a manner of' ('-ly') — that's why grisly means something that is fearfully horrible.