The Collaborative International Dictionary
Splenium \Sple"ni*um\, n.[L., a plaster, a patch, from Gr. ???? a bandage, compress.] (Anat.) The thickened posterior border of the corpus callosum; -- so called in allusion to its shape.
Wiktionary
n. 1 (context anatomy English) The rounded posterior extremity of the brain's corpus callosum. 2 (context medicine English) A compress or bandage.
Wikipedia
The posterior end of the corpus callosum is the thickest part, and is termed the splenium (Greek splenion = a bandage).
It overlaps the tela chorioidea of the third ventricle and the mid-brain, and ends in a thick, convex, free border.
A sagittal section of the splenium shows that the posterior end of the corpus callosum is acutely bent forward, the upper and lower parts being applied to each other.