dull, blunt, obtuse mean not sharp, keen, or acute.

dull suggests a lack or loss of keenness, zest, or pungency.

blunt suggests an inherent lack of sharpness or quickness of feeling or perception.

obtuse implies such bluntness as makes one insensitive in perception or imagination.

bluff, blunt, brusque, curt, crusty, gruff mean abrupt and unceremonious in speech and manner.

bluff connotes good-natured outspokenness and unconventionality.

blunt suggests directness of expression in disregard of others' feelings.

brusque applies to a sharpness or ungraciousness.

curt implies disconcerting shortness or rude conciseness.

crusty suggests a harsh or surly manner sometimes concealing an inner kindliness.

gruff suggests a hoarse or husky speech which may imply bad temper but more often implies embarrassment or shyness.