Rogue : Rascal

The relationship in the pair Rogue : Rascal is one of synonyms, as both words describe a dishonest or unprincipled person. We must find the option that shares this synonym relationship:

Option A: Murderer : Cruelty — This is a Characteristic relationship; cruelty is a trait of a murderer, but they are not synonyms.

Option B: Polite : Harsh — This is an Antonym relationship; the words have opposite meanings.

Option C: Spendthrift : Extravagant — This is a Synonym relationship; both words describe someone who spends money in a reckless or wasteful manner.

Option D: Notorious : Famous — While both mean well-known, they have opposite connotations (negative vs. positive), so they are not true synonyms in this context.
Hence the correct answer is Option C.