mesolymphocyte

[mĕz′ə-lĭmfə-sīt′]
n.
  1. A mononuclear leukocyte of medium size, probably a lymphocyte, having a deeply staining nucleus that is relatively smaller than that in most lymphocytes.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.