Where does “क्षुभ्” come from?

क्षुभ् (Sanskrit) comes from Proto-Indo-European *k⁽ʷ⁾sewbʰ-.

Ancestry of “क्षुभ्”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	*k⁽ʷ⁾sewbʰ-	—