E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
This word has greatly changed its original meaning. The Romans used it for a thanksgiving after a signal victory (Livy, iii. 63). (His rebus gestis, supplicatio a senatu decreta est [C: Bell. Gall., ii.].) The word means the act of folding the knees (sub-plico). We now use the word for begging or entreating something.