Tarjeta, Spanish for “card,” comes from the same root as target. This is only obvious in retrospect, since the interchange between the ‘j’ and the ‘g’ makes it hard to recognize. But once you learn it, it is easy to remember that the t‑r-j maps to the t‑r-g.
Both words come from the old German (via old French) targa, meaning “shield.” Yes: a target is just a shield – your shield is a target, since it is the shield that is hit, not you! And a card (tarjeta) is also a shield – just a very small one!