Source : Webster's Revised Unabridged Dictionary (1913)

Overnight \O"ver*night"\, adv.
   In the fore part of the night last past; in the evening
   before; also, during the night; as, the candle will not last
   overnight.

         I had been telling her all that happened overnight.
                                                  --Dickens.

Overnight \O"ver*night`\, n.
   The fore part of the night last past; the previous evening.
   [R.] --Shak.

Source : WordNet®

overnight
     adv : happening in a short time or with great speed; "these
           solutions cannot be found overnight!"

overnight
     adj : lasting through or extending over the whole night; "a
           nightlong vigil"; "an overnight trip" [syn: {nightlong}]