The phrase "brass eye" is an uncommon term, and as such, it is challenging to find precise synonyms. Some potential alternatives include "bold stare," "unwavering gaze," "fierce glare," and "penetrating look." These terms invoke a similar sense of intensity and scrutiny as "brass eye." However, it is essential to remember that synonyms can vary in intensity and emotional connotation, so depending on the context, some words may be more appropriate than others. Therefore, it is crucial to consider the context and tone of the sentence when selecting a replacement word for "brass eye".