The English word sibling comes from sib + ling. According to the OED the etymology of sib is:
Etymology: Old English sib(b , = Old Frisian (and Frisian) sib , Middle Dutch sib(be , zibbe , Old High German sippi (Middle High German sippe ), Gothic (un)sibjis . With the noun uses compare Old Frisian sibba , sibbe , Middle Dutch sibbe , etc., Old Saxon sibbio (Middle Low German sibbe ), Old High German sippo (German sippe , sipp ) kinsman.
Are there another other equivalents of the word sibling in other European languages which come from the same root? The German word "geschwister" for example seems to come from Middle High German geswister, from Old High German giswestar which is a different root as far as I can tell.
In fact I am not even sure which other European languages have a word for sibling. It seems that French does not but Danish has "søskende".