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early 15c., from Middle French complication, from Latin complicationem (nominative complicatio), noun of action from past participle stem of complicare "to fold together, fold up, roll up," from com- "together" (see com-) + plicare "to fold, weave" (see ply (v.1)). Meaning "something that complicates" first recorded 1903.
complication com·pli·ca·tion (kŏm'plĭ-kā'shən)
A pathological process or event occurring during a disease that is not an essential part of the disease; it may result from the disease or from independent causes.