The Collaborative International Dictionary of English v.0.48:

Bilirubin \Bil`i*ru"bin\, n. [L. bilis biel + ruber red.]
   (Physiol.)
   A reddish yellow pigment present in human bile, and in that
   from carnivorous and herbivorous animals; the normal biliary
   pigment.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bilirubin
    n 1: an orange-yellow pigment in the bile that forms as a
         product of hemoglobin; excess amounts in the blood produce
         the yellow appearance observed in jaundice [syn:
         bilirubin, hematoidin, haematoidin]