Strong grasp of a subject (7)
I believe the answer is:
mastery
(Other definitions for mastery that I've seen before include "Total control" , "Comprehensive skill" , "Acquirement" , "superior knowledge" , "dominion" .)
I believe the answer is:
mastery
(Other definitions for mastery that I've seen before include "Total control" , "Comprehensive skill" , "Acquirement" , "superior knowledge" , "dominion" .)