small blood vessel similar to a capillary but with a fenestrated endothelium. Sinusoids are found in the liver, lymphoid tissue, endocrine organs, and hematopoietic organs such as the bone marrow and the spleen. Sinusoids found within terminal villi of the placenta are not comparable to these; they possess a continuous endothelium and complete basal lamina[WP]. [ http://en.wikipedia.org/wiki/Sinusoid_(blood_vessel) ]
Synonyms: sinusoidal blood vessel sinusoidal blood vessel endothelium
Fenestrated blood vessel endothelium with pores that are large enough for blood cells to pass. The basal lamina and gap junctions may be discontinuous.[TAO]
some sources give discontinuous capillary as synonym but this may be a subtype - see FMA:63198 discontinuous sinusoid (undefined).
endothelium of irregular blood filled space