不可

Verb

 * 1)  cannot
 * 2) should not; must not
 * 1) should not; must not
 * 1) should not; must not

Usage notes
In the sense should not, is usually preceded by  in the structure, meaning must.

Etymology
The prefix.

Noun

 * 1) being bad or unacceptable
 * 2) a failing grade on a test