Formerly practicioner for *practicianer, from practician +‎ -er (the suffix unnecessarily added, as in musicianer).

• (UK) IPA^(key): /pɹækˈtɪʃənə/
• (US) IPA^(key): /pɹækˈtɪʃənəɹ/

• Audio (Southern England):

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practitioner (plural practitioners)

1. A person who practices a profession or art, especially law or medicine.

   Synonym: practician

   • 2014 June 21, “Magician’s brain”, in The Economist, volume 411, number 8892:

     The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason. The architect of modern science was himself not very modern. He was obsessed with alchemy.

2. One who does anything customarily or habitually.
   • 2023 March 5, “Four Hubei Residents Arrested for Raising Awareness about the Persecution of Falun Gong”, in Falun Dafa Information Center‎^[1], archived from the original on 14 March 2023, Persecution in China‎^[2]:

     On January 31, 2023, four Falun Gong practitioners in Songbu Town, Macheng City, Hubei Province were arrested. Two of the arrested are still detained as of February 25, 2023.

3. (dated) A sly or artful person.
   • c. 1572, John Whitgift, Admonition to the Parliament:

     […] the men of St. John's were cunning practitioners, in shaking off their Masters and Heads.

• “practitioner”, in OneLook Dictionary Search.