'tiresome' originates from English, formed from the verb 'tire' + the suffix '-some'. The verb 'tire' ultimately comes from Old French 'tirer' (originally 'to pull'), which acquired senses including 'to weary', and the suffix '-some' comes from Old English '-sum' meaning 'characterized by'.

'tire' passed into Middle English as forms like 'tirien' or 'teren' meaning 'to pull' or 'to exhaust'; its sense developed toward 'to wear out' or 'to make weary', and in Early Modern English the adjective 'tiresome' was formed by adding '-some' to describe something that causes weariness.

Initially connected with the idea of being worn out or exhausted (linked to 'pulling'/'wearing out'), it evolved to mean more specifically 'causing boredom, annoyance, or weariness' in modern usage.