As the creeds give no authoritative definition of a miracle, we must examine individual statements, in order to get the Orthodox idea.
To answer the question, What is a miracle? is not as easy as it would seem, as will appear from considering the different definitions given by different authorities, taking first those of the dictionary.
Johnson. “Miracle. A wonder—something above human power. (In theology.) An effect above human or natural power, performed in attestation of some truth.”
Webster. “Miracle. (In theology.) An event or effect [pg 059] contrary to the established constitution and course of things, or a deviation from the known laws of nature; a supernatural event.”
Robinson's Bible Dictionary. “Miracle. A sign, wonder, prodigy. These terms are commonly used in Scripture to denote an action, event, or effect, superior (or contrary) to the general and established laws of nature. And they are given, not only to true miracles, wrought by saints or prophets sent by God, but also to the false miracles of impostors, and to wonders wrought by the wicked, by false prophets or by devils.” After giving examples of this from the Scriptures, Robinson adds, “Miracles and prodigies, therefore, are not always sure signs of the sanctity of those who perform them, nor proofs of the truth of the doctrine they deliver, nor certain testimonies of their divine mission.”
American Encyclopœdia. Miracle. “It is usually defined to be a deviation from the course of nature. But this definition seems to omit one of the elements of a miracle, viz., that it is an event produced by the interposition of an intelligent power for moral purposes; for, otherwise, we must consider every strange phenomenon, which our knowledge will not permit us to explain, as a miraculous event. A revelation is itself a miracle. If one claims to be a teacher from God, he asserts a miraculous communication with God; this communication, however, cannot be visible, and visible miracles may therefore be necessary to give credibility to his pretensions. The use, then, of a miraculous interposition in changing the usual course of nature is to prove the moral government of God, and to explain the character of it.”
Theodore Parker. “A miracle is one of three things.
“1. It is a transgression of all law which God has made; or,
“2. A transgression of all known laws, or obedience to a law which we may yet discover; or,
“3. A transgression of all law known or knowable by man, but yet in conformity with some law out of our reach.”