Of definite shape and volume; not liquid or gaseous. Firm or compact in substance. Not hollowed out: a solid block of wood. Being the same substance or color throughout: solid gold. Mathematics Of or relating to three-dimensional geometric figures or bodies. Having no gaps or breaks; continuous: a solid line of people. Of good quality and substance: a solid foundation. Substantial; hearty: a solid meal. Sound; reliable: solid facts. Financially sound. Upstanding and dependable: a solid citizen. Written without a hyphen or space. For example, the word software is a solid compound. Printing Having no leads between the lines. Acting together; unanimous: a solid voting bloc. Slang Excellent; first-rate. A substance having a definite shape and volume; one that is neither liquid nor gaseous. Mathematics A geometric figure having three dimensions. As a whole; unanimously: The committee voted solid for the challenger. Without a break or opening; completely or continuously: The theater was booked solid for a month.