also, through 18c., errour; c. 1300, "a deviation from truth made through ignorance or inadvertence, a mistake," also "offense against morality or justice; transgression, wrong-doing, sin;" from Old French error "mistake, flaw, defect, heresy," from Latin errorem (nominative error) "a wandering, straying, a going astray; meandering; doubt, uncertainty;" also "a figurative going astray, mistake," from errare "to wander; to err" (see err). From early 14c. as "state of believing or practicing what is false or heretical; false opinion or belief, heresy." From late 14c. as "deviation from what is normal; abnormality, aberration." From 1726 as "difference between observed value and true value."
Words for "error" in most Indo-European languages originally meant "wander, go astray" (for example Greek plane in the New Testament, Old Norse villa, Lithuanian klaida, Sanskrit bhrama-), but Irish has dearmad "error," from dermat "a forgetting."
-less
word-forming element meaning "lacking, cannot be, does not," from Old English -leas, from leas "free (from), devoid (of), false, feigned," from Proto-Germanic *lausaz (cognates: Dutch -loos, German -los "-less," Old Norse lauss "loose, free, vacant, dissolute," Middle Dutch los, German los "loose, free," Gothic laus "empty, vain"), from PIE root *leu- "to loosen, divide, cut apart." Related to loose and lease.