spiculum

noun4

1. •
   A sharp, pointed crystal, especially of ice.
2. •
   A sharp, needle-like structure, especially those making up the skeleton of a sponge.
3. •
   A small radial emission of gas seen in the chromosphere and corona of the sun.
4. •
   A thrusting javelin used by Romans that replaced the pilum in the late 3rd century.