a step or action that is too ambitious; an act of overreaching

listen to the pronunciation of a step or action that is too ambitious; an act of overreaching
Английский Язык - Английский Язык
bridge too far

Cloning was an interesting concept. Cloning body parts was again just man's search for immortality riding on the back of naive altruistic medicinal benevolence. But cloning a person was a bridge too far.