Very Tough GCET question

Find the odd one out .

1. Terrible
2. Credible
   
3. Birbal
   
4. Sensible
   

PS. GCET is Gujarat Common Entrance Test, one of the toughest MBA entrance exams in India. One has to clear this exam to get into the prestigious Veer Narmad South Gujarat Universtity for their much sought-after MBA course.