Poker-specific term. In one sense it's a loan, but really it's more like "investing" in a player, giving them the money they don't have to buy into a game ("table stakes") in exchange for a percentage of their winnings.
I've often heard it used to mean buying a player's buy-in, in return for (hopefully) a percentage of their winnings. Often there's no obligation to pay the staker back in the event of a loss, but in the case of a large stake to a mobster, maybe it's a different story
The amount you’re playing with is called your “stake”. (Same root as “proof of stake” in crypto.)
You might stake another player (loan them the money and collect interest/vigorish). In modern high-stakes poker, you might also “buy a piece” of a player where they put up half and you put up half and split the win/loss (or have another split).
Staking, the present participle of stake, which means a wager, bet, or pledge. Tony is loaning Davey the money, but specifically to use as a wager, or stake, so it is Tony that is staking.
What does "staking with" mean here? It sounds like "loaning", but I've never heard this phrase.