This maybe a pointless, stupid thread, but I just wanna know something. here i go!

Sharin-gan, Byuku-gan, Rasen-gan. They all have the word -gan at the end. What does gan mean?
I was thinking that before Rasengan came out, I thought -gan meant 'eye'. But after Rasengan came out, i was thinking that hmm....... maybe -gan means 'ball' (since Rasengan is round like a ball, and eyes are like balls as well).