The term 'hourglass grains' refers to the small, granular particles of sand that are used to fill an hourglass. The grains are usually made of quartz, which is a mineral composed of silicon dioxide. The grains are usually uniform in size and shape, and they are often used to measure time. The crossword solution for this term is 'SANDS, ' which is a general term for any type of loose, granular material composed of small particles.