What does "Above Board", also written as "Aboveboard" really mean and when did it first appear?

Some believe the term arose from a reported practice of hiding pirates below deck - below board - while the ship's crew through all was well "above board" or on the upper deck.

The strongest evidence points to the term "Above Board" as coming from the world of gambling.

Hear all the details in this episode.
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Sources:

The Phrase Finder: https://www.phrases.org.uk/meanings/22300.html.

Merriam-Webster Online: https://www.merriam-webster.com/dictionary/aboveboard
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Host:

Stephen Carter; Email: CarterMethod@gmail.com.
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Technical Information:

Recorded and first editing done with Audacity. Final editing and rendering done with Hindenburg Journalist Pro.

Microphone: Shure SM58.

Key Words:

Aboveboard, Above Board, polymath, logophile, philomath, gambling terms,