The Collaborative International Dictionary of English v.0.48:

Verjuice \Ver"juice`\, n. [OE. vergeous, F. verjus, that is, the
   juice of green fruits; verd, vert, green + jus juice. See
   Verdant, and Juice.]
   1. The sour juice of crab apples, of green or unripe grapes,
      apples, etc.; also, an acid liquor made from such juice.
      [1913 Webster]

   2. Tartness; sourness, as of disposition.
      [1913 Webster]