What's the difference between once and quondam?

Once

Definition:

• (adv.) By limitation to the number one; for one time; not twice nor any number of times more than one.
• (adv.) At some one period of time; -- used indefinitely.
• (adv.) At any one time; -- often nearly equivalent to ever, if ever, or whenever; as, once kindled, it may not be quenched.

Example Sentences:

Quondam

Definition:

• (a.) Having been formerly; former; sometime.
• (n.) A person dismissed or ejected from a position.

Example Sentences:

• (1) At least he can protest that Rebekah Brooks, quondam chair of Women in Journalism, reassured him it was harmless.
• (2) Brodie Clark , the quondam head of the UK border force, appeared before the House of Commons home affairs committee.
• (3) Now, when the cops arrive the two quondam assailants are discovered exchanging numbers and planning to have dinner on Saturday night.