invulnerable (adj.)Related entries & more
kryptonite (n.)Related entries & more
fictional substance in the "Superman" series, where it weakens the otherwise invulnerable hero, 1943; perhaps from elements of krypton (which is a gas) + meteorite.
impregnable (adj.)Related entries & more
inviolable (adj.)Related entries & more
mid-15c., "that is to be kept without violation" (of an oath, etc.), from Latin inviolabilis "inviolable, invulnerable," from in- "not, opposite of" (see in- (1)) + violabilis "that may be injured, easily wounded," from violare "to do violence to" (see violation). Meaning "having a right or guaranty of immunity" (of a place of sanctuary, etc.) is from 1570s. Meaning "incapable of being injured" is from 1520s. Related: Inviolably.
Achilles tendon (n.)Related entries & more
from Modern Latin tendo Achillis, first used by German surgeon Lorenz Heister (1683-1758) and so-called in reference to the one vulnerable spot of the Greek hero Achilles, whose mother held him by the heel when she dipped him in the River Styx to render him invulnerable (this story is not in Homer and not found before 1c. C.E.). Earlier Achilles' sinew, from Modern Latin chorda Achillis, coined 1693 by Dutch anatomist Philip Verheyden when dissecting his own amputated leg. Hence figurative use of heel of Achillies for "vulnerable spot" (1810).