What is "all hail"

Hail \Hail\, interj. [See Hail, v. t.] An exclamation of respectful or reverent salutation, or, occasionally, of familiar greeting. ``Hail, brave friend.''
--Shak.

All hail. See in the Vocabulary.

Hail Mary, a form of prayer made use of in the Roman Catholic Church in invocation of the Virgin. See Ave Maria.

All hail \All` hail"\ [All + hail, interj.] All health; -- a phrase of salutation or welcome.

interj. All health; a phrase of salutation or welcome.