Comparative evidence

ḱei̯s

• OInd. śiṣ- 'leave' (Whitney 1885: 173); 'leave remaining' (MW: 1076)

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.