Ruthless
Part of speech: adjective
Definition: Without pity or compassion; cruel, pitiless.
Example sentence: As long as man continues to be the ruthless destroyer of lower living beings he will never know health or peace. For as long as men massacre animals, they will kill each other.
Pitiless
Part of speech: adjective
Definition: having, or showing, no pity; mercilesshaving no kindly feelings; unkind