IPA: /ˈkruːlər/
KK: /ˈkruːlər/
Having a tendency to cause pain or suffering to others; being harsh or unkind.
The crueler of the two brothers often bullied the younger one.
Comparative: crueler
Superlative: cruelest
Crueler is formed from "cruel" (from Old French *cruel*, meaning harsh or severe) and the comparative suffix "-er" (meaning more). The word "crueler" means one who is more harsh or severe than another.
Think of someone who is 'more harsh' ('cruel') — the '-er' indicates a comparison, so a crueler person is simply someone who is more cruel.