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early 15c., "action of growing out," from Latin excrescentia (plural) "abnormal growths," from excrescentem (nominative excrescens), present participle of excrescere "grow out, grow up," from ex- "out" (see ex-) + crescere "to grow" (see crescent). Meaning "that which grows out abnormally (on a living thing) is from 1570s (excrescency in this sense is 1540s).
excrescence ex·cres·cence (ĭk-skrěs'əns)
An outgrowth from a surface that may be normal, such as a fingernail, or abnormal, such as a wart.