half-wit

Naomi Watts plays Diana as a sweet-natured, wistful, half-wit.

For the instant he partially suspected mischief and wheeled about, but one look at the half-wit dissipated all doubt.

"For the family," was Cleena's watchword, and it had already become the half-wit's.

For even if one calls him a half-wit, it still makes a difference that he keeps the right half of his wits.