forbidden

 
Pronunciation: /fəˈbɪd(ə)n/

adjective

  • 1not allowed; banned: a list of forbidden books
  • 2 Physics denoting or involving a transition between two quantum-mechanical states that does not conform to some selection rule, especially for electric dipole radiation.

Phrases

the forbidden degrees

the number of steps of descent from the same ancestor that bar two related people from marrying.

forbidden fruit

a thing that is desired all the more because it is not allowed.
[with biblical allusion to Gen. 2:17]