c. 1200, "lack of wisdom or knowledge," from Old French ignorance (12c.), from Latin ignorantia "want of knowledge" (see ignorant). Ignoration (1832) has been used in the sense "act of ignoring." The proverb, in the form "Where ignorance is bliss, 'tis folly to be wise", is from Gray's "Ode on a Distant Prospect of Eton College" (1742) .
Middle English also had simplesse, from French, attested in English from mid-14c. in sense "humility, lack of pride," late 14c. as "wholeness, unity;" c. 1400 as "ignorance."
1540s, from French vincible and directly from Latin vincibilis "that which can be gained; easily maintained," from vincere "to overcome, conquer" (from nasalized form of PIE root *weik- (3) "to fight, conquer"). A vincible ignorance in theology is an ignorance in one who possesses the means of overcoming it.
early 15c., from Old French invincible (14c.) or directly from Latin invincibilis "unconquerable," from in- "not" (see in- (1)) + vincibilis "to be gained, easily maintained, conquerable," from vincere "to overcome" (from nasalized form of PIE root *weik- (3) "to fight, conquer"). Related: Invincibly.
The noun meaning "one who is invincible" is from 1630s. Invincible ignorance, an ignorance which the person having it lacks means to overcome, is from Church Latin ignorantia invincibilis (Aquinas). The Invincible Armada was the Spanish of 1588. Related: Invincibly.
early 13c., derk, "absence of light, night-time," from dark (adj.). Figurative in the dark "in a state of ignorance" is from 1670s; earlier it meant "in secrecy, in concealment" (late 14c.).
"doubtfulness, dubiousness," 1650s, from Late Latin dubietas "doubt, uncertainty," from Latin dubius "vacillating, fluctuating," figuratively "wavering in opinion, doubting" (see dubious). Earlier in the same sense were dubiosity (1640s), dubiousness (1650s); also see dubitation.
Ignorance is the mother of two filthy daughters; the first daughter of Ignorance is called dubiety, or doubtfulnesse, which is a continual wavering in opinion; a knowing man hath a fixt spirit, and settled judgement, but an ignorant man is a double-minded man, though he be never so resolute and wilful in his opinions. [W. Geering, "The Mischiefes and Danger of the Sin of Ignorance," London, 1659]