Social media repositories serve as a significant source of evidence when extracting information related to the reputation of a particular entity (e.g., a particular politician, singer or company). Reputation management experts manually mine the social media repositories (in particular Twitter) for monitoring the reputation of a particular entity. Recently, the online reputation management evaluation campaign known as RepLab at CLEF has turned attention to devising computational methods for facilitating reputation management experts. A quite significant research challenge related to the above issue is to classify the reputation dimension of tweets with respect to entity names. More specifically, finding various aspects of a brand's reputation is an important task which can help companies in monitoring areas of their strengths and weaknesses in an effective manner. To address this issue in this paper we use dominant Wikipedia categories related to a reputation dimension; the dominant Wikipedia categories are then utilised within a semantic relatedness scoring framework to generate "associativities" with respect to the various reputation dimensions, and another version of "associativity" normalized by the "content entropy" of Wikipedia categories. The Wikipedia categories obtained through our applied methods are finally used in a random forest classifier for the task of reputation dimensions classification. The experimental evaluations show a significant improvement over the baseline accuracy.