"economical in use," 1590s, from Middle French frugal, from Latin frugalis, from undeclined adjective frugi "useful, proper, worthy, honest; temperate, economical," originally dative of frux (plural fruges) "fruit, produce," figuratively "value, result, success," related to fructus (see fruit), from PIE *bhrug- "agricultural produce," also "to enjoy." Sense evolved in Latin from "useful" to "profitable" to "economical." Related: Frugally.