Dictionary of Biblical Words:
A phrase often very wrongly and lightly used—probably taken from 1 Cor. 2:16. It is not, however, generally used in this simple sense, but is intended to mean that the person who has it is not only spiritual, but knows God’s thoughts and judgment on the matter in hand—a very blessed and rare thing to have—but certainly not a matter to boast of, still less to assert in support of an opinion or line of conduct. All such expressions should be used sparingly, and with great caution.
Strong’s Dictionary of Greek Words:
Meaning:
probably from the base of 1097; the intellect, i.e. mind (divine or human; in thought, feeling, or will); by implication, meaning
KJV Usage:
mind, understanding. Compare 5590