In view of the semantic ambiguity in interpreting a concept, the definition can play a part in enriching ontological concepts and facilitating consistent interpretation and application of ontologies. Definition learning may take on various forms: identifying and extracting new definitions, selecting from alternative definitions, and compiling definitions from pieces of information. Heuristic indicators and/or patterns such as is defined as and is referred to as have been applied in learning definitions . Moreover, the large body of literature on word sense disambiguation is conducive to selecting among alternative definitions. There have been some encouraging results on interpreting new concepts based on the definitions of component words from existing resources and in learning definitions through relations. Nonetheless, the effectiveness of the above approaches needs to be evaluated formally.