Where does “мостище” come from?

мостище (Church Slavonic) comes from Proto-Slavic mostъ, from Proto-Balto-Slavic *mastás.

Ancestry of “мостище”, step by step

StepLanguageWordMeaning
1Proto-Slavicmostъbridge
2Proto-Balto-Slavic*mastás—
Every word from Proto-Balto-Slavic *mastás →Every word from Proto-Slavic mostъ →