at liberty

Free, not obligated; also, not occupied. For example, I am not at liberty to tell you the whole story, or "I ... washed when there was a basin at liberty" (Charlotte Brontë, Jane Eyre, 1847). This idiom is often used in a negative context, as in the first example. [First half of 1800s]

The adjective has 3 meanings:

Meaning #1: not under constraint of any kind
  Synonym: unconstrained

Meaning #2: having escaped, especially from confinement
  Synonyms: at large, escaped, loose, on the loose

Meaning #3: not engaged or employed or occupied