LITUUS

‖Lit″u‐us (?), n.; pl. Litui (#). [] 1. 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.
2. 2. (Math.) A spiral whose polar equation is r2θ = 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.