убы́ток (Russian) comes from Russian убы́ть, from Russian быть, from Old East Slavic бꙑти, from Proto-Slavic *byti, from Proto-Balto-Slavic bū́ˀtei, from Proto-Indo-European bʰuH- — to become, grow, appear.
убы́ток (Russian): loss, damage negative result on balance