Mesentery is the name of a whole set of tissues attaching the intestines to the abdominal wall.
In human anatomy, there are three different portions of the mesentery:
* Mesenterium sensu strictu, also called Meso
* Mesocolon transversum
* Mesocolon sigmoideum, also called Mesosigmoideum
Two smaller mesenteries can be found at the appendix (Mesoappendix), and at the cranial part of the rectum (Mesorectum)
So... Mesocolon is a part of the mesentery, but no synonym.