The Collaborative International Dictionary of English v.0.48:

thujone \thu"jone\ (th[=u]"j[=o]n), n.
   An oil, C10H16O, the chief constituent of cedar leaf oil
   (thuja oil), which is obtained from the northern white cedar
   (arbor vitae, Thuja occidentalis) or the western Red Cedar
   (Thuja plicatis). It is a stimulant similar to camphor. It
   is also called thujol, thuyol, absinthol, thuyone,
   tanacetol, and tanacetone. --Stedman.
   [PJC]