Today’s idiom: safe as houses
Meaning: perfectly safe, certain
Origin: The general consensus is that phrase came about in reference to investments, that investing in buildings is a safe move because of the tendency for the value to appreciate. Another source said that the phrase came from less literal origins. It points out that “safe” is probably referring to assuredly and cites the many examples of when safe is used in phrases: “safe enough to be hanged,” “safe to thunder,” “safe as the bellows.” The first written instance of the phrase is found in 1859.