scutum

noun5

1. •
   (historical) An oblong shield made of boards or wickerwork covered with leather, with sometimes an iron rim; carried chiefly by the heavily armed infantry of the Roman army.
2. •
   A scute.
3. •
   A shield-like protection, such as the scutum protecting the back of a hard tick (cf. alloscutum, conscutum).

   • A tick's eye, if present, is a mere roundish lucent area at the margin of the scutum about opposite the second coxa. — 2009
4. •
   One of the two lower valves of the operculum of a barnacle.
5. •
   The kneecap.