Answer:
You can use a thesaurus for the prominent words of the definition, which can locate synonyms or related words. Many online dictionaries will provide entries if a search is done for the definition.
You may also find the word through one or more answers on WikiAnswers.
In brief, try to zero in on a keyword in your definition. Then look up that keyword in a dictionary. Read the whole reference and you will likely find the defining word or the concept that you are looking for.