IPA: /ˈfɪə.sə.mli/
KK: /ˈfɪr.sə.mli/
In a way that causes fear or is frightening.
The monster roared fearsomely, sending shivers down everyone's spine.
Fearsomely → It is formed from "fear" (from Old English "fǣr", meaning a feeling of anxiety or dread) and the suffix "-some" (meaning characterized by or causing). The word "fearsomely" means in a manner that causes fear or dread.
Think of the feeling of 'fear' and how something 'causes' that feeling ('-some'). This helps you remember that 'fearsomely' describes something done in a way that inspires fear.