no-go

Short definition from Wiktionary

Adjective

1. 1
   Not functioning properly.
2. 2
   Not to be entered.
3. 3
   That should not go (i.e., enter or engage) if the size of the part being measured is properly achieved.
4. 4
   Alternative form of no-go.

Noun

1. 1
   A no-go gauge.
2. 2
   Alternative form of no go.
3. 3
   Something which should not or cannot be done.