What's the difference between i.e. and e.g.?
"authoritative sanction," 1630s, from Latin fiat "let it be done" (also used in the opening of Medieval Latin proclamations and commands), third person singular present subjunctive of fieri, used as passive of facere "to make, do" (see factitious). Also sometimes a reference to fiat lux "let there be light" in the Book of Genesis.