From Turkish karın (“womb”) -daş (“fellow, sharer”). karındaş with the meaning ‘pregnant’ which got a semantic shift into modern karnaş and kardeş meaning ‘sibling’ i.e. wombmates from karın (womb, abdomen, stomach-please).
kardeş (definite accusative kardeşi, plural kardeşler)
There is no distinction between brother and sister in Turkish.
Gender is specifically indicated if a distinction is necessary; erkek kardeş (literally “boy/man sibling”) means “brother” and kız kardeş (literally “girl sibling”) means “sister”.