insuperable

mid-14c., “unconquerable,” from Latin insuperabilis “that cannot be passed over, unconquerable,” from in- “not, opposite of” (see in- (1)) + superabilis “that may be overcome,” from superare “to overcome,” from superus “one that is above,” from super “over” (see super-). Figurative use from 1650s. Related: Insuperably.