Staight as a Die

[lolding]

Where does the saying "Straight as a Die/Dye" come from?

[Quizmonster]

A 'die' is the singular form of 'dice'...ie a cube with numbers/pictures etc on each of the six sides, used in gaming of various forms. In order to be fair, these had to be 'straight'...ie true and genuinely shaped rather than biassed or false.

[Quizmonster]

A die was also a tool for stamping out coins, so that, too, had to be exactly truly-shaped.

[nescio]

To Quizmonster
Straight as a die does refer to dice (singular), but straight in this sense means unbiassed, in the sense that when a die is cast, each number is exactly equally likely to come up.

[searchme]

A Die is also a tool used to cut a thread on a preformed metal rod in order to make a bolt.(As in a Tap and Die set)

The Die has to positioned exactly straight in order to function effectively.

[Quizmonster]

Nescio, I actually used the phrase "rather than biassed" in my earlier response! In addition I referred to fairness...that is, surely, "equally likely to come up", as you yourself put it!
Sorry, but I really fail to see what you have added in response to the question. But what the hey!

[albatross521]

I reckon it means absolutely honest, reliable.