The merging or assimilation of several different traditions, especially in the theology and mythology of religion, thus asserting an underlying unity; the reconciliation or fusion of differing systems of belief such as in philosophy or religion.

Or, in the words of Umberto Eco in Foucault’s Pendulum:

“Syncretism is the acknowledgement that a single tradition runs through and nurtures all religion, all learning, all philosophy. The wise man does not discriminate; he gather together all the shreds of light, from wherever they may come.”