[randommodnar]

Also, sibling is not a 20th century invention in gender neutrality. Sibling is an old English word meaning a kinsmen or relative. It simply saw a revival in the 20th century and had its meaning narrowed to mean only brother or sister.

[roywiggins]

You're right, but when people began to hear it again in the 20th century, they didn't think "ah, I know that word! It's Old English." It wasn't, at the beginning of the 20th Century, an English word at all.

I'm not sure reintroducing a word from a long-dead language (even if it's an antecedent to your own) is much different from just making a new word up, other than it might sound a bit better if the language is related. Words can come from anywhere; why not invent the ones you need? Laser radar quark...