It has been shown that while multiple unrelated meanings of a word (e.g. bank) increase processing latency, polysemy, that is multiple related word senses (e.g. paper) produce faster responses (Rodd, Gaskell & Marslen-Wilson, 2002; Klepousniotou, 2002). The goal of this study was to explore the effect of polysemy on word processing in Serbian. The outcomes of three lexical decision experiments have shown that polysemous words are processed faster. In addition, lemma frequency and number of related senses did not interact. Finally, a measure that combines lemma frequency and number of related senses into a single metric is proposed. This measure is information residual, initially applied on derivational morphology (Moscoso del Prado Martìn, Kostic & Baayen, 2004). In this study the information residual is a difference between the amount of information (bit) derived from lemma frequency and the entropy of a polysemic cluster. Since relative frequencies of different word senses of a given word in Serbian are currently not available, maximum entropy (log N) was used as an approximation. The outcome of this study indicates that cognitive system is sensitive not only to the entropy of derivational clusters, but polysemic clusters as well.