inerrant (adj.)

1650s, in reference to "fixed" stars (as opposed to "wandering" planets), from Latin inerrantem (nominative inerrans) "not wandering, fixed (of stars)," from in- "not, opposite of" (see in- (1)) + errans, present participle of errare "to wander, stray, roam, rove" (see err). Meaning "unerring, free from error" is from 1785.