Definitions: (1) strength derived from vigorous growth, determination of spirit, or solidity of constitution <a person of sturdy stock>; robust; hardy; (2) courageous; indomitable; resolute

Idiom: Sturdy as an oak

Quote: The key to every man is his thought. Sturdy and defying though he look, he has a helm which he obeys, which is the idea after which all his facts are classified. He can only be reformed by showing him a new idea which commands his own. — Ralph Waldo Emerson (1803-1882) American Poet

Observation: Even if a person is as sturdy as an oak, you can tell by their smile if they have a gentle spirit.