Comparative evidence

kseu̯bʰ, kʷseu̯bʰ

• OInd. kṣubh- 'quake' (Whitney 1885: 30); 'shake', 'tremble', 'be agitated', 'be disturbed', 'be unsteady', 'stumble' (literally and metaphorically) (MW: 331)

References

MW = Monier-Williams, M. 1899. A Sanskrit-English Dictionary. Clarendon Press.
Whitney 1885 = Whitney W. D. 1885. The roots, verb forms and primary derivatives of the Sanskrit language. A supplement to his Sanskrit grammar. Leipzig.