英语词源字典 - 在线词源网站

frugal (adj.)[frugal 词源字典]: "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.[frugal etymology, frugal origin, 英语词源]
Morton: surname, from the many Mortons on the map of England, literally "moor or marsh settlement." Morton's Fork (1759) is in reference to John Morton (c. 1420-1500), archbishop of Canterbury, who levied forced loans under Henry VII by arguing the obviously rich could afford to pay and the obviously poor clearly were living frugally and thus had savings and could pay, too.
plainly (adv.): late 14c., from plain (adj.) + -ly (2). Meaning "simply, frugally" is from 1560s.