noun A large solid piece of hard material, especially rock, stone, or wood, typically with flat surfaces on each side. (a block of marble) A large single building subdivided into separate rooms, apartments, or offices. (an apartment block) A large quantity or allocation of things regarded as a unit. (
a block of shares) An obstacle to the normal progress or functioning of something. (substantial demands for time off may constitute a block to career advancement) A flat area of something, especially a solid area of color. (cover the eyelid with a neutral block of color) A pulley or system of pulleys mounted in a case. (a simple pulley block) A person's head.