Question: is pusillanimous a real word?
Answer: It doesn't make sense grammatically. Pusillanimous is an adjective — a describing words — not a noun. In the same way you can't say “Don't be a quiet” or “Don't be a small” or “Don't be a green” or “Don't be a spicy”, you can't say “Don't be a pusillanimous.” You can't tell people not to be a/an adjective.