Source : Webster's Revised Unabridged Dictionary (1913)

Retinaculum \Ret`i*nac"u*lum\, n.; pl. {Retinacula}. [L., a
   holdfast, a band. See {Retain}.]
   1. (Anat.)
      (a) A connecting band; a fr[ae]num; as, the retinacula of
          the ileoc[ae]cal and ileocolic valves.
      (b) One of the annular ligaments which hold the tendons
          close to the bones at the larger joints, as at the
          wrist and ankle.

   2. (Zo["o]l) One of the retractor muscles of the proboscis of
      certain worms.

   3. (Bot.) A small gland or process to which bodies are
      attached; as, the glandular retinacula to which the
      pollinia of orchids are attached, or the hooks which
      support the seeds in many acanthaceous plants.