Select the option that can be used as a one-word substitute for the given group of words.
A lover of mankind

The correct answer is Philanthropist.

Let's understand the meaning of the given group of words and analyze each option:
"A lover of mankind" refers to someone who seeks to promote the welfare of others, especially by the generous donation of money to good causes. This is represented by the word Philanthropist.

We can also break down the word Philanthropist into its Greek roots:
1. phil- (or philo-) means "loving" or "dear".
2. anthrop- (from anthropos) means "human" or "mankind".
Combining these gives "one who loves mankind".

Let's look at why the other options are incorrect:
- Recluse: A person who lives a solitary life and tends to avoid other people.
- Cynic: A person who believes that people are motivated purely by self-interest rather than acting for honorable or unselfish reasons.
- Psychiatrist: A medical doctor who specializes in diagnosing, treating, and preventing mental, emotional, and behavioral disorders.