from 1 (as a negative particle) and 5424; properly, mindless, i.e. stupid, (by implication) ignorant, (specially) egotistic, (practically) rash, or (morally) unbelieving:

KJV-- fool (-ish), unwise.

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5424 phren (frane);

probably from an obsolete phrao (to rein in or curb; compare 5420); the midrif (as a partition of the body), i.e. (figuratively and by implication, of sympathy) the feelings (or sensitive nature; by extension [also in the plural] the mind or cognitive faculties):

KJV-- understanding.