Well, it's kind of a complex question. 'Why' is a word in English that's traditionally used to ask for the reason or purpose behind something.
'Why' sounds a little weird now that I think about it.
That's true, the more you think about the same word, the more it starts to sound strange. It's called 'semantic satiation.'
That's fascinating. But why does 'why' specifically mean what it means?
Like most words, 'why' comes from older languages. In this case, it comes from the Old English word 'hwi', which also meant 'for what reason'. Language evolves over time, and 'hwi' eventually became 'why' in Modern English.