Masterly

Part of speech: adjective (a.)

1. Suitable to, or characteristic of, a master; indicating thorough knowledge or superior skill and power; showing a master's hand; as, a masterly design; a masterly performance; a masterly policy. "A wise and masterly inactivity." Sir J. Mackintosh.

2. Imperious; domineering; arbitrary.

Part of speech: adverb (adv.)

With the skill of a master. Thou dost speak masterly. Shak.