Our second to last word: yes.
Yes comes from the Old English gise/gese, which meant “so be it”. The first syllable, whether ge or gi, comes from the Old English word ge, which means so or yes and comes from the Proto Germanic ja/jai (another way of saying yes) and the Proto Indo European yam. The -se part of the word is from si, the third person form of to be that’s used in commands. So we just shortened a way of saying “so be it” and now it’s the most common way for agreeing to something.
And for the record, a lot of words beginning with Y began with G in Old English. It must have something to do with the pronunciation of G back then.
Tony Jebson’s page on the Origins of Old EnglishUniversity of Texas at Austin Linguistic Research Center