plication. n. 1. (Biology) the act of folding or the condition of being folded or plicate. 2. (Geological Science) a folded part or structure, esp a fold in a series of rock strata. 3. (Surgery) surgery the act or process of suturing together the walls of a hollow organ or part to reduce its size. (plaɪˈkeɪ ʃən, plɪ-). n.