A distinction is sometimes made between sanitarium (a kind of health resort, as in the Battle Creek Sanitarium) and sanatorium (a hospital). However, in America, the term sanatorium was often used throughout the 20th century as a socially acceptable term for psychiatric hospitals.
The traits of a gentleman include: A gentleman is generous with his time, wisdom, and resources. He willingly serves others and extends a hand to those in need. A gentleman possesses a positive outlook on life.
In Britain, it means diddly. It means you're a male, presumably respectable. If you have no other title, then the overly-British will put esq. after your name on an envelope, etc. In America, I believe it's sometimes used after a lawyer's surname. However, I don't see it used much by U.S. lawyers.