This is the 12454th most frequent Russian word.
кипятка
"Boiling water."
The word 'кипятка' (genitive case of 'кипяток') here refers to a quantity of boiling water.
Налей мне стакан кипятка, пожалуйста.
Pour me a glass of boiling water, please.
'Кипятком' (instrumental case of 'кипяток') is used to describe the object causing the burn.
Осторожно! Он обжёгся кипятком.
Be careful! He burned himself with boiling water.
'Кипятка' (genitive case of 'кипяток') denotes the quantity of boiling water required.