The paper shows that a predominance of plural forms of a noun over its singular forms often indicates a semantic distinction between them. We argue that, in the case of nouns whose plural forms express collective meaning and nouns whose plural forms tend to be interpreted as mass names, this semantic distinction is of a grammatico-lexical nature. Plural forms expressing collective meaning may be semantically specified with a phrase containing a categorial noun (jedny cigarety = jedna krabička cigaret ‘one pack of cigarettes’). Due to their semantic relationship to plural forms with a non-collective meaning, the opposition between singular and plural morphology is not fully neutralized (as in the case of pluralia tantum), but only partially so. The close relationship between plural forms inclined toward a mass interpretation (maliny ‘raspberries’; piliny ‘sawdust’) and proper mass nouns is proven by the fact that they are combined with the same type of quantifiers and measure phrases. The paper also shows how the semantics of nouns with predominantly plural morphology is reflected in the Academic Dictionary of Contemporary Czech (Akademický slovník současné češtiny or ASSČ) which is currently being compiled.