I like how Kanji (the Chinese characters) can give nice meanings to words. This is a pretty basic word and I knew it a few days after starting to learn Japanese but only recently learned this way of writing it with Kanji.
Meaning: an egg
Kanji: ball + child
And come to think of it, an egg is exactly that - a ball containing a child.
I think it's elegant, this whole meaning into words using Kanji thing.
This word also has it's own Kanji (卵) and honestly, I have no idea when to use which one and whether or not there's a difference, I just liked the ball-child combination for the word.