Proficience, Proficiency, n.
The quality of state of being proficient; advance in the acquisition of any art, science, or knowledge; progression in knowledge; improvement; adeptness; as, to acquire proficiency in music.
Shades of meaning
Fernald has no entry of its own for proficiency; he lists it under progress.
Where he writes about it:
Attainment, development, and proficiency are more absolute than the other words of the group, denoting some point of advantage or of comparative perfection reached by forward or onward movement; we speak of attainments in virtue or scholarship, proficiency in music or languages, the development of new powers or organs; proficiency includes the idea of skill. — from progress