The word arrant is best utilized to emphasize the extremeness of a negative trait. It is often paired with nouns representing undesirable characteristics to convey complete and utter expression of that trait. It effectively strengthens the negative connotation of the term it modifies, and its usage is predominantly found in literary or rhetorical contexts to deliver a powerful impact.

The word errant is commonly used to describe someone or something that deviates from a set path or norm. It often carries a connotation of wandering or roaming, sometimes with a sense of misguidedness or error. The term can also imply a romantic or chivalrous notion of adventure, as seen in historical references to 'knights errant.'

To distinguish between arrant and 'errant,' remember that arrant emphasizes the extreme negative aspects of something, akin to saying 'thoroughly bad.' On the other hand, errant often describes a person or object that strays from the accepted path, potentially losing their way or engaging in a noble quest. Although both adjectives, their applications differ greatly—one describes degree of negativity, and the other a type of behavior. The next time you encounter these terms, consider the context to determine which word is appropriate for reinforcing the intended meaning.