The Collaborative International Dictionary of English v.0.48:

Atilt \A*tilt"\, adv. [Pref. a- + tilt.]
   1. In the manner of a tilter; in the position, or with the
      action, of one making a thrust. "To run atilt at men."
      --Hudibras.
      [1913 Webster]

   2. In the position of a cask tilted, or with one end raised.

   Note: [In this sense sometimes used as an adjective.]
         [1913 Webster]

               Abroach, atilt, and run
               Even to the lees of honor.         --Beau. & Fl.
         [1913 Webster]

WordNet (r) 3.0 (2006):

atilt
    adj 1: departing or being caused to depart from the true
           vertical or horizontal; "the leaning tower of Pisa"; "the
           headstones were tilted" [syn: atilt, canted,
           leaning, tilted, tipped]