"working or acting for reward, serving only for gain," hence "resulting from sordid motives, ready to accept dishonorable gain," 1530s, from mercenary (n.), or in part from Latin mercenarius "hired, paid, serving for pay."
c. 1300, undermyne, "render unstable by digging at the foundation," from under + mine (v.1) "dig." The figurative sense "injure by invisible, secret, or dishonorable means" is attested from early 15c. Similar formation in Dutch ondermijnen, Danish underminere, German unterminiren. The Old English verb was underdelfan. Related: Undermined; undermining.
c. 1300, revilen, "debase, degrade" (a sense now obsolete);" mid-14c., "insult, taunt, vilify, assail with abusive language," from Old French reviler "consider vile, despise, scorn," from re-, here perhaps an intensive prefix (see re-), + aviler "make vile or cheap, disesteem," from vil "shameful, dishonorable; low-born; cheap; ugly, hideous" (see vile (adj.)). Related: Reviled; reviler; reviling.
The term implies the habitual frequenting of places where wagers are made and games of chance are played, and the seeking of subsistence by dishonorable betting, but does not always imply direct cheating. Sometimes contracted to leg. [Century Dictionary]
Used from 1865 of strike-breakers and workmen who refused to join trade unions.
late 14c., "disgraceful, shameful, without honesty or integrity; unjust, unfair, disposed to deceive or cheat; unmodest, unchaste," from Old French deshoneste (13c., Modern French déshonnête) "dishonorable, horrible, indecent," perhaps from a Medieval Latin or Gallo-Roman compound of Latin dis- "not" (see dis-) + honestus "honorable; deserving honor, respectable," from honos "honor, dignity, office, reputation," which is of unknown origin. The Latin formation was dehonestus. Related: Dishonestly.