Answer:
A synonym for mastery might be proficiency or comprehension.
Step-by-step explanation:
Mastery means to have "comprehensive knowledge or skill in a subject or accomplishment. " (Source: Oxford).
Proficiency means to have "a high degree of competence or skill; expertise. " (Source: Oxford).
Comprehension means to have "the action or capability of understanding something. ".
Comprehension may be more mental focused than the connotation of mastery, but it still fits.