Concepts that are semantically equivalent. Model can use different terms to refer to the same concept or the same properties are modelled differently by different terms.

Goh, Cheng Hian. Representing and reasoning about semantic conflicts in heterogeneous information systems. Diss. Massachusetts Institute of Technology, 1996. [http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.139.5885&rep=rep1&type=pdf]