1
general::
1. Also, at one's ease. Comfortable, relaxed, unembarrassed, as in I always feel at ease in my grandmother's house. The related idiom put at ease means "make comfortable, reassure," as in I was worried that the letter would not arrive in time, but the postmaster put me at ease. [1300s] For the antonym, see ILL AT EASE. 2. In a relaxed position in military ranks. The phrase is often used as a command for troops standing at attention to relax, as in At ease, squadron. The command stand at ease is slightly different. A British military dictionary of 1802 described it as standing with the right foot drawn back about six inches and one's weight put on it. An American version is to stand with one's feet slightly apart and the hands clasped behind one's back.
American Heritage Idioms
2
general::
Phrase(s): at ease
without worry or anxiety. • The performer is at ease on the stage. • After she had met a few people, Mary felt at ease with the group.
McGrawhill's American Idioms And Phrasal Verbs