Complete, utter, or absolute; used to emphasize that something is bad or wrong in the most extreme way.
From Middle English and Old French 'errant', meaning wandering or roving, from 'errer' (to wander). The meaning shifted to 'extreme' or 'utter' in the 14th-15th centuries, possibly influenced by association with 'errant' knights.
Arrant is one of the only surviving uses of the old word 'errant' (as in 'knight errant'), but the meanings diverged—while 'errant' kept its 'wandering' sense, 'arrant' evolved to mean something completely different: absolute badness.
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