Early last century, Henry and Francis Fowler coined the phrase elegant variation to refer to needless "substitutions of one word for another for the sake of variety" (The King's English, 1906). Given a choice between "monotonous repetition on the one hand and clumsy variation on the other," we're advised to prefer "the natural… to the artificial."
In other words, to ensure that our writing is clear and direct, we shouldn't be afraid to repeat words.
Similar advice was offered decades later by New York Times editor Theodore M. Bernstein, who coined his own terms for the fear of repetition and the excessive use of distracting synonyms:
Definition: An overwhelming fear of using a word more than once in a single sentence, or even in a single paragraph.
Etiology: As a child the patient was probably compelled to stand in a corner because he wrote, in a composition: "Grandma gave me a piece of apple pie, then I had another piece of apple pie and then I had another piece of apple pie."
Symptoms: The patient now writes: "The wife gave me a piece of apple pie, then I obtained another slice of the pastry containing the round fleshy fruit, and then I secured another portion of the all-American dessert." As is evident, monologophobia is usually accompanied by synonymomania.
Treatment: Gently suggest to the patient that repetition is not necessarily fatal, but that if it is an intrusive manifestation, the corrective is not a conspicuous synonym but rather an inconspicuous pronoun or noun: "another," "a second," "a third one."
(Miss Thistlebottom's Hobgoblins, Farrar, Straus and Giroux, 1971)
A monologophobe, Harold Evans has said, would edit the Bible to read, "Let there be light and there was solar illumination" (Essential English, 2000).
Of course, needless repetition is often just clutter that can be readily avoided without indulging in synonymomania. But not all repetition is bad. Used skillfully and selectively, the repetition of key words in a paragraph can help to hold sentences together and focus the reader's attention on a central idea.