Prince Turveydrop sometimes played the kit, dancing; sometimes played the piano, standing; sometimes hummed the tune with what little breath he could spare, while he set a pupil right; always conscientiously moved with the least proficient through every step and every part of the figure; and never rested for an instant.
There are no more uses of "proficiency" in the book.
Show samples from other sources
Not as well as my mother, but I’m pretty proficient."
Kiera Cass -- The Heir
Yvette was by far the most competent of my coworkers, and she and I would often work together on any electrical job requiring proficiency with tools.