Is gambling or playing the lottery a sin?

The straight answer

There is no verse that says do not gamble. There are several that describe exactly what gambling is built on, and they are not encouraging.

Wealth from nothing dwindles, while wealth gathered by labour grows. A faithful person will be rich in blessings, but whoever is in a hurry to be rich will not go unpunished. Do not wear yourself out to get rich. Chasing fantasies leads to poverty. None of those are about lotteries specifically, and none of them can be turned into a rule that a raffle ticket at a church fair is sin.

Two things push harder than the verses about hurry. The first is who pays. Lottery spending takes a far larger share of income from low-income households, which makes it a transfer from people with the least margin to a state budget, and Scripture is relentless about profit taken from the poor. The second is what it does to you: a game engineered so the house always wins is designed to keep you playing, and Proverbs is full of warnings about appetite that cannot be satisfied.

So: not named as sin, and not defensible as a plan. If you play, treat it as entertainment you have already spent, never as a financial strategy, and watch who is funding the prize.