Source : Webster's Revised Unabridged Dictionary (1913)

Alas \A*las"\, interj. [OE. alas, allas, OF. alas, F. h['e]las;
   a interj. (L. ah.) + las wretched (that I am), L. lassus
   weary, akin to E. late. See {Late}.]
   An exclamation expressive of sorrow, pity, or apprehension of
   evil; -- in old writers, sometimes followed by day or white;
   alas the day, like alack a day, or alas the white.

Source : WordNet®

alas
     adv : by bad luck; "unfortunately it rained all day"; "alas, I
           cannot stay" [syn: {unfortunately}, {unluckily}, {regrettably}]
           [ant: {fortunately}, {fortunately}]