c. 1300, "deceitfulness, treachery, faithlessness, dishonesty," from false + -ness.

c. 1300, falshede, "deceitfulness," also "a lie; that which is false," from false + -hood. Formed on the same pattern are Old Frisian falschede, Dutch valschheid, German Falschheit, Swedish falskhet. Former noun forms in English, now extinct, included falsage "wrongdoing" (late 15c.), falsdom "deceitfulness, treachery; a lie" (c. 1300), fals-lek "falsehood" (early 14c.), falsshipe "deceitfulness, dishonesty" (c. 1200).

"full of deceit, tending to mislead," mid-15c., from deceit + -ful. Earlier in the same sense was deceivant (late 14c.). Related: Deceitfully; deceitfulness.

c. 1300, "deceitfulness, treachery, dishonesty," from Old French fauseté "falsehood" (12c., Modern French fausseté), from Late Latin falsitatem (nominative falsitas), from Latin falsus "erroneous, mistaken" (see false). From late 14c. as "untrue statement or doctrine;" from 1570s as "character of being not true."

c. 1300, "mechanical device," especially one used in war; "manner of construction," also "skill, craft, innate ability; deceitfulness, trickery," from Old French engin "skill, wit, cleverness," also "trick, deceit, stratagem; war machine" (12c.), from Latin ingenium "innate qualities, ability; inborn character," in Late Latin "a war engine, battering ram" (Tertullian, Isidore of Seville); literally "that which is inborn," from in- "in" (from PIE root *en "in") + gignere, from PIE *gen(e)-yo-, suffixed form of root *gene- "give birth, beget."

Sense of "device that converts energy to mechanical power" is 18c.; in 19c. especially of steam engines. Middle English also had ingeny (n.) "gadget, apparatus, device," directly from Latin ingenium.

c. 1300, "trickery, treachery, lying," from Old French deceite, fem. past participle of deceveir, decevoir, from Latin decipere "to ensnare, take in, beguile, cheat," from de "from" or pejorative (see de-) + capere "to take," from PIE root *kap- "to grasp."

From mid-14c. as "act or practice of deceiving," also "false appearance, illusion." From late 14c. as "quality of being false or misleading."

Deceit is a shorter and more energetic word for deceitfulness, indicating the quality; it is also, but more rarely, used to express the act or manner of deceiving. The reverse is true of deception, which is properly the act or course by which one deceives, and not properly the quality; it may express the state of being deceived. Fraud is an act or series of acts of deceit by which one attempts to benefit himself at the expense of others. It is generally a breaking of the law; the others are not. [Century Dictionary]