Proficient, adept, skilled, skillful, expert, masterly are comparable when they mean having the knowledge and experience necessary to success in a given line especially of work or endeavor.
When applied to things rather than persons, all these terms carry the implication that the quality of the person has been attributed to the thing.
Proficient implies training and practice as the source of competency beyond the average.
Adept implies proficiency but stresses aptitude and often cleverness.
Skilled, often interchangeable with proficient, may distinctively suggest mastery of the details of a trade or handicraft or of the technique of an art or profession. In modern industrial use skilled simply connotes that one has met a standard set up by employers for a special type of work or job.
Skillful implies adeptness coupled with dexterity in execution or performance.
Expert applies to one who has attained extraordinary proficiency or is exceptionally adept.
Masterly, applied more often to the thing executed or the quality displayed than to the person who executes or displays, is close to expert in its implication of proficiency and adeptness, but it commonly adds a suggestion of confident control.