In Polish, if you are having a ‘shot of vodka’ you would order po pięćdziesiątce meaning to take ‘by fifties‘. This refers to the common size of a shot being 50 mL in Poland. An American shot is about 44 mL or 1.5 ounces. In Russia they say соtка for a double shot meaning 100 (mL).
Why do we call it a shot here in the States? Contrary to some folk etymologies, there were no guns involved in the naming. Rather, it uses shot to mean a small dose of something.