Source : Webster's Revised Unabridged Dictionary (1913)

Anarthrous \An*ar"throus\, a. [Gr. 'a`narqros without joints,
   without the article; 'an priv. + 'a`rqron joint, the
   article.]
   1. (Gr. Gram.) Used without the article; as, an anarthrous
      substantive.

   2. (Zo["o]l.) Without joints, or having the joints
      indistinct, as some insects.