ash (tree)
梣 refers specifically to the ash tree, a type of deciduous tree known for its strong wood.
梣 combines 木 (tree) with 岑, which likely contributes the sound and may relate to a steep hill, but the exact historical development is uncertain.
The tree radical 木 beside 岑 (which looks like a mountain with a peak) suggests a tall, strong tree growing on a steep slope: an ash tree.
For シン, imagine the ash tree's wood being used to make a shin guard: shin -> シン, protecting your leg like the tough ash wood.
common ash (Fraxinus excelsior); European ash