liquidate v.

late 14c., "flowing, capable of flowing; neither solid nor gaseous," from Old French liquide "liquid, running" (13c.), from Latin liquidus "fluid, liquid, moist," figuratively "flowing, continuing," also of sounds and voices, from liquere "be fluid," related to liqui "to melt, flow," from PIE *wleik- "to flow, run."

In English, of sounds from 1630s. Financial sense of "capable of being converted to cash" is first recorded 1818, from earlier use in Scots Law (17c.) in reference to debts that had been proved (in court, etc.).

1570s, in law, of debts, noun of action from past-participle stem of Late Latin liquidare "melt, make liquid" (see liquidate). Originally as a legal term in reference to assets; of companies going out of business, 1869; of inconvenient groups of persons, "a killing, a wiping out," 1925 in communist writings. In O. Henry, "the act of taking a drink of liquor."

1825, agent noun in Latin form from liquidate (v.). By 1949 in the "killer" sense.