1. By accident
   - haply [archaic], by luck 
2. Without advance planning
   - accidentally, circumstantially, unexpectedly 
3. [archaic] Through chance, "To sleep, perchance to dream.."
   - perchance [archaic]

Encyclopedia: By chance

• viscose rayon
• viscosimeter
• viscosimetric
• viscosimetry
• viscosity
• viscount
• Viscount Nelson
• Viscount Northcliffe
• Viscount St. Albans
• viscountcy
• viscountess
• Viscountess Astor
• viscounty
• viscous
• viscousness
• Viscum
• Viscum album
• viscus
• vise
• viselike
• Vishnu
• Vishnuism
• visibility
• visible
• visible balance