To Flunk

1. (US, transitive, intransitive) Of a student, to fail a class; to not pass.

2. (US, transitive) Of a teacher, to deny a student a passing grade.

3. (US, dated, informal) To shirk (a task or duty).
4. To back out through fear. (Commonly in the phrase 'flunk it', the 'it' referring to a specific task avoided; sometimes without specific reference describing a person's attitude to life in general.)1.