from
The Collaborative International Dictionary of English v.0.48
Lituus \Lit"u*us\, n.; pl. {Litui}. [L.]
1. (Rom. Antig.)
(a) A curved staff used by the augurs in quartering the
heavens.
(b) An instrument of martial music; a kind of trumpet of a
somewhat curved form and shrill note.
[1913 Webster]
2. (Math.) A spiral whose polar equation is r^{2}[theta] = a;
that is, a curve the square of whose radius vector varies
inversely as the angle which the radius vector makes with
a given line.
[1913 Webster]