Gambling is impossible to win at and involves you slowly losing money to the house. Poker is a game with skill involved where you can make money off other players.
Poker is a good reason why your definition is incorrect. Poker is gambling, but it doesn't resemble you slowly losing your money to the house. I mean, that happens too, but it resembles slowly losing your money to the other players.
Unless you're in the small % of winning players, then it looks like gambling where you slowly win money from the other players.