"to cover the surface of (something)," c. 1300, in part from Old English oferlecgan "to place over," also "to overburden," and in part from over- + lay (v.). There also was an overlie in Middle English, but it merged into this word. Similar compounds are found in other Germanic languages, such as German überlegen, Dutch overlegen, Gothic ufarlagjan. Related: Overlaid; overlaying.
late 14c., oppressen, "to press unduly upon or against, overburden, weigh down," also figuratively, "overwhelm overpower" (of sickness, grief, etc.); also "burden with cruel, unjust, or unreasonable restraints, treat with injustice or undue severity, keep down by an unjust exercise of power," from Old French opresser "oppress, afflict; torment, smother" (13c.), from Medieval Latin oppressare, frequentative of Latin opprimere "press against, press together, press down;" figuratively "crush, put down, subdue, prosecute relentlessly" (in Late Latin "to rape"), from assimilated form of ob "against" (see ob-) + premere "to press, hold fast, cover, crowd, compress" (from PIE root *per- (4) "to strike"). In Middle English also "to rape." Related: Oppressed; oppressing.
It is the due [external] restraint and not the moderation of rulers that constitutes a state of liberty; as the power to oppress, though never exercised, does a state of slavery. [St. George Tucker, "View of the Constitution of the United States," 1803]