The term 'roof support beam' is a structural element of a building that provides support for the roof. The crossword solution for this term is 'RAFTER, ' which is a sloping beam that runs from the ridge of the roof to the wall plate or eave of the building. Rafters are typically made of wood and are used to support the weight of the roof. They also provide stability and strength to the structure, helping to prevent it from collapsing.