Extremely tedious, monotonous, and depressing; causing weariness and gloom.
From 'dreary' (Old English 'dreore', meaning gory or bloody, later meaning dull) combined with '-some' (Old English suffix meaning 'characterized by'). The suffix '-some' was added to intensify the negative quality, similar to 'tiresome' or 'lonesome'.
This is a rare, almost archaic way to describe extreme boredom—it's like someone in the 1600s looked at 'dreary' and thought 'this needs to be even MORE depressing.' Writers like Byron used '-some' words to create a moral or emotional weight that modern synonyms just don't carry.
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