grain

The smallest unit of mass in the three English systems (avoirdupois, troy, and apothecaries' weights) used in the UK and USA, equal to 0.0648 g. It was reputedly the weight of a grain of wheat. One pound avoirdupois equals 7,000 grains; one pound troy or apothecaries' weight equals 5,760 grains.

grain

In a piece of timber, the mass of plant cells in the heartwood compressed together as the cells die. It is seen as long thin strands when the wood is cut. The grain runs in one direction. Timber has a high tensile strength along the grain.