big, great
鉅 centers on largeness or greatness, often with a nuance of something massive or substantial, like a huge piece of metal.
鉅 combines 金 (metal) with 巨 (huge), suggesting a large metal object or the idea of greatness associated with metal. The exact historical development is uncertain, but the phono-semantic structure is plausible.
Picture a giant metal (金) ingot so huge (巨) that it takes several people to lift it. That massive piece of metal represents something big and great.
For キョ, imagine a huge metal key (キー) that is so big it looks like a giant's key: key -> キョ, and the giant metal key embodies the kanji's meaning of big and great.