Where does “исполинский” come from?

исполинский (Russian) comes from Russian исполи́н, from Old Church Slavonic исполинъ, from Proto-Slavic *jьspolinъ.

исполинский (Russian): gigantic

Definitions

Step	Language	Word	Meaning
1	Russian	исполи́н	—
2	Old Church Slavonic	исполинъ	giant
3	Proto-Slavic	*jьspolinъ	—

исполинский — Etymology, Origin & Word History | Etymology Explorer