Unerring is from un- ('not') + erring, present participle of err, from Old French errer, from Latin errare ('to wander, stray, go astray'), from Proto-Indo-European *ers- ('to be in motion'). Important recorded forms include un- (Old English), errare (Latin), and *ers- (Proto-Indo-European). Morphologically, the un- element marks negation, reversal, removal, or deprivation, while the base supplies the action, quality, or state being denied or undone. The modern sense continues the older lexical line without requiring a separate origin. In current use it covers consistently accurate and never making a mistake. The wider family includes derived forms such as unerringly and related words such as err, error, and erring.