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

• effects
• platen
• plater
• plateresque
• platform
• platform bed
• platform game
• platform rocker
• platformer
• Plath
• Platichthys
• Platichthys flesus
• platina
• plating
• platinise
• platinize
• platinous
• platinum
• platinum black
• platinum blond
• platinum thermometer
• platinum-blonde
• platitude
• platitudinal
• platitudinarian