Something tiresome annoys you slowly. It is not exciting anger — it is the feeling of "oh, this again". A long form with too many boxes is tiresome. A colleague who tells the same story every week is tiresome. Waiting on the phone for forty minutes is tiresome. The word is an adjective and works both for things (a tiresome journey, tiresome paperwork) and for people and their behaviour (a tiresome child, don't be tiresome). Notice the small trap in the spelling: it comes from tire, but it does not mainly mean "makes your body tired". It means "wears out your patience". A tiresome meeting may involve no physical work at all. If your legs ache after climbing, that is tiring, not tiresome. The word feels a bit formal and a bit old-fashioned, and it has a British flavour — you hear it more from older speakers and read it more in books than you hear it from young people in the street. Young speakers would say annoying, or a pain, or such a hassle. That does not make tiresome wrong; it makes it polite. It is the word you choose when you are complaining but do not want to sound rude.