1610s, "that may or must be deplored, lamentable, grievous, miserable;" from 1640s as "pitiable, wretched, contemptible," 1610s, from -able + deplore (v.) "lament, bewail, give up as hopeless," from French déplorer (13c.), from Latin deplorare "bewail, lament, give up for lost," from de- "entirely" (see de-) + plorare "weep, cry out," which is of unknown origin.
Perhaps from or inspired by French déplorable or directly from Late Latin deplorabilis. "It is sometimes, in a more lax and jocular sense, used for contemptible; despicable: as deplorable nonsense; deplorable stupidity" [Johnson, 1755]. Related: Deplorably; deplorableness; deplorability.
As a noun it is attested from 1830 as "deplorable ills." Deplorables was used politically in reference to the ministry of Charles X of France in the 1820s (le ministère déplorable). Rare in 19c.-20c.; in U.S. it got a boost 2016 when used by presidential candidate Hillary Clinton in reference to supporters of her rival, Donald Trump, some of whom embraced it as a despite-word.