Is “Mastery” a Scrabble word?
Yes
MASTERY
Valid in at least one Scrabble dictionary
Valid in these dictionaries
SOWPODS / CSW
Scrabble UK & International
TWL / NWL
Scrabble North America
Large English Dictionary
General English word list
Meaning of Mastery
/ˈmɑːst(ə)ɹi/
noun
1.The position or authority of a master; dominion; command; supremacy; superiority.
2.Superiority in war or competition; victory; triumph; preeminence.
3.Contest for superiority.