liquid (adj.)
late 14c., from Old French liquide "liquid, running," from Latin liquidus "fluid, liquid, moist," figuratively "flowing, continuing," from liquere "be fluid," related to liqui "to melt, flow," from PIE *wleik- "to flow, run." Of sounds, from 1630s (the Latin word also was used of sounds). Financial sense of "capable of being converted to cash" is first recorded 1818.
liquid (n.)
"a liquid substance," 1709, from liquid (adj.). Earlier it meant "sound of a liquid consonant" (1520s).