Comparative evidence

2.ḱei̯

• OInd. śī- 'fall' (Whitney 1885: 173); 'fall out', 'fall away', 'disappear', 'vanish' (MW: 1077)

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.