arrow
箭 centers on a projectile shot from a bow: an arrow. It is a specific term for the arrow itself, distinct from the bow.
箭 combines 竹 (bamboo) with 前, which likely contributes the sound. Bamboo was historically used for arrow shafts, so the character represents an arrow made of bamboo.
Bamboo 竹 on top of 前: picture a bamboo shaft with a pointed tip flying forward (前 means 'front' or 'before'), like an arrow shot ahead.
For セン, imagine a sen (銭, an old coin) tied to the arrow's shaft for a high-stakes archery contest: sen -> セン, and the arrow flies with the coin attached.