As Heinz Lueneburg noted, "lakh" is from Sanskrit "laksha".
Similarly, "crore" is from Sanskrit "koti". These terms for
10E5 and 10E7 are attested in non-mathematical works in epic and
dharmasastra literature going back to the first few centuries of
this era; they seem to have got into Sanskrit scientific texts a few
centuries later. Cf. Takao Hayashi, _The Bakhshali Manuscript_,
Gronigen 1995, chapter 6.
Kim Plofker
Dept. of History of Mathematics
Brown University
Providence, RI 02912 USA