1. in a way that inspires fear or dread; terrifyingly
2. in a way that is impressively large, powerful, or formidable

Examples

• The storm approached fearsomely, with lightning splitting the sky.
• The boxer fearsomely dominated his opponent in the ring.
• The ancient castle loomed fearsomely over the village below.
• She fearsomely defended her position in the debate.
• The predator's teeth gleamed fearsomely in the darkness.
• The company fearsomely expanded its market share last year.