Fearsome (adjective)

1. Inspiring fear or awe; formidable.
2. Frightening; terrifying.

Origin:

Middle english fear + -some, from old english færsum.

Examples:

1. The fierce storm had a fearsome appearance.
2. The notorious gang leader had a fearsome reputation.
3. The giant snake was so fearsome that people were afraid to approach it.
4. The old castle had a fearsome look, as if it was haunted.
5. The thunderous roar of the lions made their presence felt and was truly fearsome.