noun
plural grains
[noncount] :the seeds of plants (such as wheat, corn, and rice) that are used for food
a plant that produces grain [count]
[count] a small, hard piece of something
a very small amount of something
[count] the way the lines or fibers in something (such as wood) are arranged - usually singular
the way that the surface of something feels when it is touched - usually singular
[count] :a unit of weight equal to 0.0648 grams
against the grain
To be/go against the grain is to be different or to act in a way that is different from what is normal or usual.
If something goes against your grain, it does not seem right or natural to you.