historicist
Well-known
This is funny, I was just thinking - if you're so interested in boredom, why don't you open encyclopedia and find the definition there? And what I have found? The word boredom is not that old – mid 19th century – probably people in the past had not been so bored to think about it.
I was quite surprised by this, but the word is indeed fairly recent. But 'ennui' is first noted for 1667, and the first recorded use is one specifically mentioning the lack of an English equivalent for the French word - I would imagine that before this educated English speakers simply used the French or Latin.