lituus

noun3

1. •
   An augur's staff with a recurved top.
2. •
   A military trumpet.

   • 1786: Fig. 3. A Roman Lituus, or military trumpet, such as is mentioned by Horace in his first ode. — Francis Grose, A Treatise on Ancient Armour and Weapons, page vi. — 1786
3. •
   A curve with polar equation r²θ=a², where a is a constant.