Dull, humdrum, dreary, monotonous, pedestrian, stodgy mean so unvaried and uninteresting as to provoke boredom or tedium.
Dull vs Blunt vs Obtuse
Dull, blunt, obtuse are comparable when they mean the reverse of sharp, keen, and acute.
Due vs Desert vs Merit
Due, desert, merit are comparable when they mean what is justly owed to a person (sometimes a thing), especially as a recompense or compensation.