weak-minded

adjective2

1. •
   Having or exhibiting a mind that lacks steadfastness, resoluteness or especially judgment; not strong-minded.

   • Stupid, she told herself. Vain, weak-minded, and stupid. — 2009
2. •
   (offensive, historical) Mentally or intellectually deficient; feeble-minded; half-witted.

   • Their mother is insane ; father somewhat weak-minded. — 1899