In this study we investigated whether and how the cognitive system uses morphological markedness of animacy and gender pairs. In the Serbian language masculine nouns are marked for animacy (i.e., genitive-accusative syncretism), while for feminine nouns the animacy distinction is purely semantic. Thus, in Experiment 1 we used this natural, linguistic differentiation to test whether morphological markedness of animacy influences lexical processing. In the same experiment, we tested whether the cognitive system is sensitive to the fact that some animate nouns have a sibling in the other gender (e.g., dečak /”boy”/ - devojčica /”girl”/), while others do not have it (e.g., vojnik /”soldier”/ or žirafa /”giraffe”/). We labeled this indicator sibling presence. The analysis did not confirm the effect of animacy, neither between nor within genders. However, animate nouns with a sibling were processed faster than those without a sibling. Since the majority of sibling nouns are morphologically related (like konobar /”waiter”/ - konobarica /”waitress”/), while the rest are not (e.g., petao /”rooster”/ - kokoška /”hen”/), in Experiment 2 we tested whether morphological relatedness contributed to the effect of sibling presence. Results showed that this is not the case: morphologically related and unrelated masculine-feminine pairs of nouns (siblings) were processed equally fast. Furthermore, an interaction between the target’s frequency and the frequency of its sibling was observed: nouns with a more frequent sibling benefited more from their own frequency than those with a less frequent sibling. We argue that sibling support is realized through semantic, not morphological relations. Taken together, our findings suggest that morphological markedness is not used in lexical processing, which is in line with an amorphous approach to lexical processing.