This is the 13342nd most frequent Russian word.
мышьяка
The Russian word "мышьяка" refers to "arsenic" in English.
The word 'мышьяка' refers to 'arsenic,' a poisonous chemical element. Here, it is used as a direct object indicating the substance found.
Доктор подтвердил наличие мышьяка в организме пациента.
The doctor confirmed the presence of arsenic in the patient's body.
In this sentence, 'мышьяка' refers to the presence of arsenic as part of the substance contained in the object being discussed.
На ярлыке бокала была предупреждающая надпись о содержании мышьяка.
The label on the glass had a warning about the content of arsenic.
Here, 'мышьяком' is the instrumental case form of 'мышьяк,' indicating the means or topic of discussion — arsenic, and shows how declensions can affect meaning.