The Collaborative International Dictionary of English v.0.48:

Lambdoid \Lamb"doid\, a. [Gr. ?, la`mbda the letter lambda
   ([Lambda]) + e"i^dos shape.]
   Shaped like the Greek letter lambda ([Lambda]); as, the
   lambdoid suture between the occipital and parietal bones of
   the skull.
   [1913 Webster]