The Collaborative International Dictionary of English v.0.48:

Acronyc \A*cron"yc\, Acronychal \A*cron"ych*al\, a. [Gr.
   'akro`nychos at nightfall; 'a`kros + ny`x night.] (Astron.)
   Rising at sunset and setting at sunrise, as a star; --
   opposed to cosmical.
   [1913 Webster]

   Note: The word is sometimes incorrectly written acronical,
         achronychal, acronichal, and acronical.
         [1913 Webster]