You can buttress an argument with solid facts or your financial portfolio with safe investments. You may find that giving compliments to everyone you meet buttresses your popularity. To buttress is to sustain or reinforce.
A buttress is a structure that adds stability to a wall or building, and this innovation played a significant role in the evolution of architecture. Think of a medieval cathedral. It's an incredibly tall, open building filled with light from vast windows. Without buttresses supporting the walls and carrying the weight of the ceiling away from the building and down to the ground, this cathedral would be impossible. Picture this when you use buttress figuratively as a verb meaning to strengthen and support.