1. In a believable manner
   "he acted believably sincere" 
2. Easy to believe on the basis of available evidence
   - credibly, plausibly, probably, tenably

See also: believable

Antonym: unbelievably

• somehow
• someone
• someplace
• somersault
• somersaulting
• somerset
• Somerset Maugham
• somesthesia
• somesthesis
• something
• sometime
• sometimes
• someway
• someways
• somewhat
• somewhen
• somewhere
• somite
• Somme
• Somme River
• sommelier
• sommer
• somnambulate
• somnambulation
• somnambulism