Is there a word missing from our language?

[AndiFlatland]

As BROTHER is to FRATERNITY, and SISTER is to SORORITY...

So what's the equivalent for SIBLING?

I don't think there is one - at least, none of my friends can think of one.

Anyone want to venture a new word for the English language and dictionary?

[Sandy-Wroe]

Sibling and siblings seem adequate

[Clanad]

Seems to me that your mixing definitions. Granted, time once was (say 1780 in the French Revolution) that fraternity may have meant brotherhood as in blood related (even then a political stretch and connivance)... however the word has morphed to mean a social organization for like minded men (same applies to sister/sorority), whereas sibling has always and continues to carry the express meaning of sisters and brothers related by blood (or, perhaps adopiton)...

[Kakuro1]

What word would you use for 'the state of being brothers' then, Clanad?

[Quizmonster]

Well, sib is the basic word from which we get sibling and the appropriate connected noun is sibship. Both The Oxford English Dictionary and Chambers list it, so there is no need at all for anyone to invent a new word. Simples!

[MarkRae]

> What word would you use for 'the state of being brothers' then, Clanad?

What's wrong with 'brotherhood'?

"Brotherhood - noun. The kinship relation between male offspring."

[Kakuro1]

MarkRae - what is wrong with fraternity?

[heathfield]

A search through a thesaurus comes up with the word ''Brood''

[ABerrant]

Germanity

[AndiFlatland]

Thanks everybody for your answers, and my apologies for not responding. I used to get an automated e-mail from the Answer Bank every time somebody responded - but this doesn't seem to happen any more, so I just assumed that there were no responses.
There still doesn't seem to be any definitive answer to my question, and I suspect that there is no such word. A friend of mine suggested that there may be a possible answer in either finding the Latin for 'sibling' (the roots of 'fraternity' and 'sorority' are the Latin words 'frater' and 'soror'), but there seems to have been no such word in the Latin language.
There is also one language (at least) in which there is a plural noun which means 'brothers and sisters'. I thought it might be German, but all my memory dredges up from my 45-years-ago learning of German is 'gebreudern' and 'geschwestern' - 'brothers' and 'sisters'. There is, I feel certain, a language in which there is a single word for both, and from which we could perhaps invent a satisfactory English word.
Any more thoughts here?

[Quizmonster]

What on earth is wrong with sibship? The OED defines sib in genetic terms as (quote) "a brother or sister or another individual of the same parentage" and 'ship' is a perfectly standard 'state' type ending as in kinship, relationship etc. Far from there being "no such word", sibship is a PERFECT such word!

[ABerrant]

Germanus = sibling

[Canary42]

Why not CLUB ?