In a manner that is extremely tedious, monotonous, and depressing.
Adverbial form of 'drearisome', created by adding '-ly' (Old English '-lice', meaning 'in the manner of'). The '-ly' suffix transforms the adjective into an adverb describing how an action is performed.
Adding '-ly' to an already rare adjective makes this word almost extinct in modern English—it's the kind of thing you'd find in dusty Victorian novels describing characters trudging through endless gray landscapes.
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