lierne rib

from The Collaborative International Dictionary of English v.0.48

Lierne rib \Lierne" rib`\ (ly[^a]rn" r[i^]b`) n. [F. lierne.]
   (Arch.)
   In Gothic vaulting, any rib which does not spring from the
   impost and is not a ridge rib, but passes from one boss or
   intersection of the principal ribs to another.
   [1913 Webster]