theta Meaning, Definition & Usage

  1. noun the 8th letter of the Greek alphabet

WordNet

The"ta noun
Etymology
L., fr. Gr. qh^ta, the Greek letter θ, Θ.
Definitions
  1. A letter of the Greek alphabet corresponding to th in English; -- sometimes called the unlucky letter, from being used by the judges on their ballots in passing condemnation on a prisoner, it being the first letter of the Greek qa`natos, death.

Webster 1913