The Catholic Encyclopedia, Volume 13: Revelation-Stock

Revelation may be defined as the communication of some truth by
God to a rational creature through means which are beyond the
ordinary course of nature. The truths revealed may be such as
are otherwise inaccessible to the human mind -- mysteries, which
even when revealed, the intellect of man is incapable of fully
penetrating. But Revelation is not restricted to these. God may
see fit to employ supernatural means to affirm truths, the
discovery of which is not per se beyond the powers of re...