'Bethnal' comes from Blithehale: a 'happy corner', or the corner of a man called Blitha.
Blithehale or Blythenhale is the earliest form of the name, from Old English healh, a corner or nook, and blithe, happy, or the personal name Blitha. The 'happy corner' may have been a clearing beside a natural spring. John Stow wrote Blethenal Green in 1598. The green was the village common; much of it survives as Bethnal Green Gardens.