1.
If something is ~, you are not allowed to do it or have it.
Smoking was ~ everywhere...
It is ~ to drive faster than 20mph.
ADJ: usu v-link ADJ, oft it v-link ADJ to-inf
2.
A ~ place is one that you are not allowed to visit or enter.
This was a ~ area for foreigners.
ADJ: usu ADJ n
3.
Forbidden is used to describe things that people strongly disapprove of or feel guilty about, and that are not often mentioned or talked about.
The war was a ~ subject...
Divorce? It was such a ~ word.
= taboo
ADJ: usu ADJ n