sharp: an edge keen enough to cut at a touch, said of a blade about to be used
Every time this word describes an edge in the New Testament, the thing named is a blade held by a heavenly figure, and all six of those verses stand in the book of Revelation. There is no sharp knife on a table and no sharp thorn in a field. The word turns up only where a weapon or a tool is being brought into use.
Two objects carry it. One is the long sword that comes out of the mouth of the risen Christ. It is described twice over, as cutting both ways (δίστομος) and as keen, so the picture is of a blade that meets no resistance from either side. Because it comes out of his mouth, the edge belongs to what he says: the sentence he speaks is the thing that cuts. The picture is borrowed from Isaiah 49:2, where the prophet's mouth is made like a sharp sword.
The other object is a harvest sickle, held first by the figure seated on the cloud and then by an angel who comes out of the temple. Harvest is an old picture for judgment, and the keen edge is part of its urgency: the crop is ripe, the blade is ready, and the swing will not be slowed. In both scenes the word says less about the metal than about how little stands in the way once the blade is used.