cashier n.

1590s, "money box;" also "money in hand, coin," from French caisse "money box" (16c.), from Provençal caissa or Italian cassa, from Latin capsa "box" (see case (n.2)); originally the money box, but by 18c. the secondary sense of the money in it became sole meaning.

Like many financial terms in English (bankrupt, etc.), it has an Italian heritage. Not related to (but influencing the form of) the colonial British cash "Indian monetary system, Chinese coin, etc.," which is from Tamil kasu, Sanskrit karsha, Sinhalese kasi.

Cash-crop "agricultural product grown to sell for profit" is attested from 1831; cash-flow from 1954; the mechanical cash-register "machine for automatically recording the sums of money deposited in it" is from 1875. 

Proto-Indo-European root meaning "to cut."

It forms all or part of: caret; cashier (v.) "dismiss;" cassation; caste; castellan; castellated; Castile; castle; castigate; castrate; castration; chaste; chastity; chateau; chatelaine; Chester; forecastle; incest; quash (v.) "make void, annul."

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sastra- "knife, dagger;" Greek keazein "to split;" Latin carere "to be cut off from," cassus "empty, void;" Old Church Slavonic kosa "scythe."