IPA: /ʌnˈmɜːrsɪfəl/
KK: /ʌnˈmɜr.sɪ.fəl/
Showing no kindness or forgiveness; very harsh or cruel.
The unmerciful storm caused great destruction in the town.
Unmerciful → It is formed from "un-" (meaning not) and "merciful" (from Old French *merciful*, meaning full of mercy). The word "unmerciful" means not full of mercy or lacking compassion.
Think of 'not' ('un-') being added to 'full of mercy' — that's why unmerciful means lacking compassion.