When it comes to finding synonyms for the term "hard masters," it is important to consider the specific context in which it is being used. In some cases, "tough instructors" or "demanding teachers" may be appropriate alternatives. Alternatively, "strict mentors" or "rigorous trainers" could also be applicable synonyms. When used in a professional setting, "challenging supervisors" or "exact managers" may be more appropriate. It is always important to consider the nuances of language and how different synonyms can convey slightly different shades of meaning. Ultimately, the choice of synonym will depend on the intended tone and purpose of the communication.