E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Native wit, a ready reply; the wit which our mother gave us. In ancient authors the term is used to express a ready reply, courteous but not profound. Thus, when Louis XIV. expressed some anxiety lest Polignac should be inconvenienced by a shower of falling rain, the mother-wit of the cardinal replied, It is nothing, I assure your Majesty; the rain of Marly never makes us wet.