Tedious, dull, or tiresome in a way that makes you want to yawn and lose interest.
From 'bore' (to cause tedium, from uncertain origin, possibly meaning 'to make a hole in someone's attention') plus the English adjective suffix '-some' meaning 'characterized by'.
The word 'bore' as tedium is actually quite young in English—it only appeared around the 1700s, possibly from the idea of drilling into someone's patience until their mind becomes hollow and empty.
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