Tedium is the dull, heavy feeling you get when something goes on and on and nothing about it changes. It is a noun, and it names the feeling itself, not the thing that causes it — so you feel tedium, you don't 'do a tedium'. It is uncountable: 'the tedium of the job', never 'a tedium' or 'tediums'. The word points at a very particular kind of boredom: not the boredom of having nothing to do, but the boredom of doing the same small thing again and again — copying numbers, waiting in a queue, driving a straight road for four hours. Length and sameness are both part of it. Most often you meet it in the phrase 'the tedium of', followed by the thing that causes it: the tedium of the flight, the tedium of housework, the tedium of a long illness. Also very common is 'relieve / break / escape the tedium' — people talk about tedium mostly when they are describing how they survived it: 'She played podcasts to break the tedium of the drive.' The word is a little formal, a little literary. In speech a Taiwanese student would more naturally say 'it was so boring', and that is fine; tedium is what you write, or what you say when you want to sound slightly wry about your suffering. Note the family around it: the adjective 'tedious' is much commoner than the noun, and 'tedious' describes the thing ('a tedious meeting'), while 'tedium' names the feeling ('the tedium of the meeting'). Though actually — English speakers do sometimes stretch it to the situation itself, saying 'the tedium of the afternoon' when they mean the afternoon was full of nothing. Nobody objects.