The article discusses the Balto-Slavic word *šama- ‘sheat-fish, Silurus glanis’ > Russian, Ukrainian, Bulgarian сом, Serbo-Croatian сoм, Slovenian sòm, Czech, Slovakian sumec, Polish sum, Low Sorbian som, Lithuanian šãmas, Latvian sams, which is problematic from the point of view of etymology. Giving an indepth analysis of previous hypotheses, the article suggests turning to the already known lexical material recorded in dictionaries. On semantic concretisation (detection of Proto-semes) of the examples and drawing from the dialects of the Slavic and Baltic languages, the old etymology of this word (Proto-Indo- European *k’em- ‘stick, pole, horn’) becomes linguistically well-reasoned.