Elegant variation.
It is the second-rate writers, those intent rather on expressing
themselves prettily than on conveying their meaning clearly, and still
more those whose notions of style are based on a few misleading rules
of thumb, that are chiefly open to the allurements of elegant
variation. ... The fatal influence ... is the advice given to young
writers never to use the same word twice in a sentence -- or within 20
lines or other limit.
-- Henry W. Fowler. Modern English Usage. (1926)