The Collaborative International Dictionary of English v.0.48:

Leucocyte \Leu"co*cyte\ (l[=u]"k[-o]*s[imac]t), n. [Leuco- + Gr.
   ky`tos a hollow vessel.] (Physiol.)
   A colorless corpuscle, as one of the white blood corpuscles,
   or those found in lymph, marrow of bone, connective tissue,
   etc.
   [1913 Webster]

   Note: They all consist of more or less spherical masses of
         protoplasm, without any surrounding membrane or wall,
         and are capable of motion.
         [1913 Webster] Leucocythaemia

WordNet (r) 3.0 (2006):

leucocyte
    n 1: blood cells that engulf and digest bacteria and fungi; an
         important part of the body's defense system [syn:
         leukocyte, leucocyte, white blood cell, white cell,
         white blood corpuscle, white corpuscle, WBC]