fiercely UK /ˈfɪəsli/US /ˈfɪɹsli/ adverb2 •In a fierce manner.The wind blew fiercely and the rain fell heavily. •Extremely; to a large degree.Because their daughter was fiercely independent and living on her own, they avoided calling that weekend. — 2026 formsfiercelier · more fiercely · fierceliest · most fiercely