1895, formed in English from plate + diminutive suffix -let.
platelet plate·let (plāt'lĭt)
n.
A minute, irregularly shaped, disklike cytoplasmic body found in blood plasma that promotes blood clotting and has no definite nucleus, no DNA, and no hemoglobin. Also called blood platelet, thrombocyte.
Small, flat disks in the blood that aid in clotting.