GAIN, in architecture, is the workmens term for the beveling shoulder of a joist or other timber. It is used, also, for the lapping of the end of the joist, &c. upon a trimmer or girder; and then the thickness of the shoulder is cut into the trimmer, also beveling upwards, that it may just receive the gain; and so the joist and trimmer lie even and level with the surface. This way of working is used in floors and hearths.