flunk

Short definition from Wiktionary

Verb

1. 1
   Of a student, to fail a class; to not pass.
2. 2
   Of a teacher, to deny a student a passing grade.
3. 3
   To fail any challenge
4. 4
   To shirk (a task or duty).
5. 5
   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.)