The Collaborative International Dictionary of English v.0.48:

Thyrsoid \Thyr"soid\ (th[~e]r"soid), Thyrsoidal \Thyr*soid"al\
   (th[~e]r*soid"al), a. [Gr. ?; ? thyrsus + e'i^dos form,
   shape: cf. F. thyrso["i]de.]
   Having somewhat the form of a thyrsus.
   [1913 Webster]