You say ‘good-bye’ and I say ‘hello.’
Or more interestingly:
You say ‘good-bye’ and I say ‘あばよ.’
Tired of the same ole 「さようなら」? Or is 「またね」 not cool enough for you anymore? Here are two ways to say ‘good-bye’; both of which aren’t very useful, but may spice up your Japanese with your friends!

1) さらば saraba

Essentially this has the same origin as 「左様なら」 【さようなら】. The 「さ」 (written with the kanji for left – 左) apparently acted like the modern 「そう」 to mean, ‘like that.’ You can often hear 「左様」 used in Jidai flicks to mean, ‘like that’ or ‘that’s right.’ (様) meaning ‘kind’ or ‘like’ here.
Originally pronounced as 「さあらば」, it adds 「さ」 (like that) with あらば (あれば if that is the case)

2) あばよ abayo

This doesn’t seem to be in usage much any more. To Yumi, it sounds like a word that would have been popular when her parents were children. But this is all the more reason to use it!
The origin of this word seems to be a mystery, but there are a few educated guesses.

  • Educated Guess #1: Comes from baby talk 「あばあば」 with a 「よ」 stuck at the end for good measure.
  • Educated Guess #2: Comes from a corruption of 「塩梅良う」 an bai you which means, “(I hope) Everything is fine” like 「よろしく」. [This isn’t too useful, but 塩梅 may occasionally be heard.]  The ‘anbai’ could also be from 按配 which has the same pronunciation and means ‘condition.’
  • Educated Guess #3: Comes from a corruption of the above 「さらば」 with a 「よ」 stuck at the end for good measure.

And Good-bye comes from ‘God be with ye’:

From Etymonline.com
1591, from godbwye (1573), itself a contraction of God be with ye, infl. by good day, good evening, etc.