dull
/ˈdəl/
adjective
tedious, uninteresting
lacking sharpness of edge or point
not resonant or ringing
dull lectures
verb
to make dull
to become dull
dull a knife's edge
adjective
mentally slow : dim-witted
He tried to teach her how to pronounce his last name with a French twirl, and when her tongue could not master it he accused her of being dull-witted.