Source : Webster's Revised Unabridged Dictionary (1913)

Potluck \Pot"luck`\, n.
   Whatever may chance to be in the pot, or may be provided for
   a meal.

         A woman whose potluck was always to be relied on. --G.
                                                  Eliot.

   {To take potluck}, to take what food may chance to be
      provided.

Source : WordNet®

potluck
     n : whatever happens to be available especially when offered to
         an unexpected guest or when brought by guests and shared
         by all; "having arrived unannounced we had to take
         potluck"; "a potluck supper"