smoke: the visible cloud of gas and fine particles given off by something burning
This is the ordinary word for smoke, and it means exactly what the English word means: the grey or dark haze that rises when something burns. There is no hidden second sense to sort out. Every occurrence points to real, visible smoke.
What makes the word worth a second look is not its definition but the company it keeps. Almost all of its appearances are in Revelation, where smoke is one of the book's recurring sights, and it shows up in scenes that could not be more different in mood. It is the smoke of incense carrying the prayers of God's people upward (Revelation 8:4), and the smoke that fills the temple when God's glory descends (Revelation 15:8). It is also the smoke pouring out of the abyss to darken the sun (Revelation 9:2), the smoke of a ruined city seen from far off (Revelation 18:9), and the smoke of torment that "goes up forever and ever" (Revelation 14:11; 19:3).
So the weight a reader feels in any given verse comes from what is burning, not from the word itself. The one occurrence outside Revelation, in Peter's sermon (Acts 2:19), quotes the prophet Joel's promise of "blood and fire and columns of smoke" as a sign of the coming day of the Lord. That same imagery reaches back to the Hebrew word for smoke, עָשָׁן, which describes both the smoke of destruction and the smoke that veiled God at Sinai.