The term may appear with various suffixes to indicate its syntactical function.

The two most common plural forms are IKHWAN (used mostly for brothers in the non-literal sense of intimate associates) and IKHWA (used mostly for blood brothers; also pronounced UKHWA).

The double form, (which means two brothers), is AKHAWAN or AKHAWAYN, depending on syntax. There is no English equivalent for this form.

The feminine form, corresponding to “sister,” is UKHT.

The double form of UKHT is UKHTAN or UKHTAYN, depending on syntax. The plural is AKHAWAT.

Please notice that the terms for “brother of” and “sister of” (as well as the terms for “father of” and “mother of”) are often used metaphorically for genitive (or possessive) relationships. For instance, AKHU KARAMA simply means a “[man] of dignity.”

I hope this is sufficient.

Fuad

I think Fuad's answer is more than sufficient, but I'd like to add the word:
shaqeeq: شقيق
In Arabic, when you say that some one is shaqeeqi شقيقي
(my shaqeeq - my brother), this means he is your brother from the same mother and father.
The word akh: أخ (brother) in this case means he is akhi: أخي (my brother), but not from the same father or the same mother.

I hope it helps you
Yacine