One who is neither intelligent nor dull
A
Tolerable
B
Commoner
C
Mediocre
D
Diligent
Correct Answer: Mediocre
One word substitute is Mediocre.Tolerable: able to be endured.
Commoner: one of the ordinary or common people, as opposed to the aristocracy or to royalty.
Mediocre: of only average quality; not very good.
Diligent: having or showing care and conscientiousness in one's work or duties.