1) Acidly 2) Bitingly 3) Fiercely 4) Harshly 5) Heartlessly 6) Nastily 7) Pitilessly 8) Spitefully 9) Unkindly 10) Unsympathetically 1) Appallingly 2) As a sadist would 3) Atrociously 4) Brutally 5) Callously 6) Cold-bloodedly 7) Contemptibly 8) Despicably 9) Excessively 10) Ferociously 11) Fiercely 12) Hard-heartedly 13) Harshly 14) Heartlessly 15) How villains act 16) In an inhuman manner 17) Inhumanly 18) Insensitively 19) Mercilessly 
• (adv.) Extremely; very. • (adv.) In a cruel manner.
Cru'el·ly adverb 1. In a cruel manner. 2. Extremely; very. [ Colloq.] Spectator. 
[adv] - in a cruel manner 2. [adv] - under cruel circumstances
adverb under cruel circumstances; `a cruelly bitter winter`