Noun

(en noun)

One who operates.

*

, title=(The Celebrity), chapter=1 , passage=The stories did not seem to me to touch life. […] They left me with the impression of a well-delivered stereopticon lecture, with characters about as life-like as the shadows on the screen, and whisking on and off, at the mercy of the operator .}}

A telecommunications facilitator whose job is to establish temporary network connections.

(mathematics) A function or other mapping that carries variables defined on a domain into another variable or set of variables in a defined range.

Chinese whispers.

(informal) A person who is adept at making deals or getting results, especially one who uses questionable methods.

A member of a military Special Operations unit.

(computing) The administrator of a channel or network on IRC.

(linguistics) A kind of expression that enters into an a-bar movement dependency and is said to bind a variable.

In the sentence "What did Bill say he wants to buy?", "what" is an operator , binding a phonetically empty variable.

Noun

(en noun)

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

*{{quote-magazine, date=2014-06-21, volume=411, issue=8892, magazine=(The Economist)

, title= Magician’s brain , passage=The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason.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.}}

One who does anything customarily or habitually.

(label) A sly or artful person.

* John Whitgift

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