Tobi roughly translates to jump or kite. We know that Tobi was the unofficial leader of Taka which means hawk. 鳶が鷹を生む, tobi ga taka o umu is roughly the mix of Tobi and Taka. This is a Japanese proverb that translates to 'A hawk born from a kite.' which is a metaphorical term for a prodigious child born from normal parents. This refers to Obito, who doesn't seem to have any known parents and if he did, they probably wouldn't be overly powerful. This could refer to Sasuke because he is a prodigy but was born to Fugaku and Mikoto and Fugaku being the Uchiha Clan Leader means he was probably very powerful. This is why Obito, under a mask was named Tobi, by Kishimoto.