The Collaborative International Dictionary of English v.0.48:

Vinegar \Vin"e*gar\, n. [OE. vinegre, F. vinaigre; vin wine (L.
   vinum) + aigre sour. See Wine, and Eager, a.]
   1. A sour liquid used as a condiment, or as a preservative,
      and obtained by the spontaneous (acetous) fermentation, or
      by the artificial oxidation, of wine, cider, beer, or the
      like.
      [1913 Webster]

   Note: The characteristic sourness of vinegar is due to acetic
         acid, of which it contains from three to five per cent.
         Wine vinegar contains also tartaric acid, citric acid,
         etc.
         [1913 Webster]

   2. Hence, anything sour; -- used also metaphorically.
      [1913 Webster]

            Here's the challenge: . . . I warrant there's
            vinegar and pepper in't.              --Shak.
      [1913 Webster]

   Aromatic vinegar, strong acetic acid highly flavored with
      aromatic substances.

   Mother of vinegar. See 4th Mother.

   Radical vinegar, acetic acid.

   Thieves' vinegar. See under Thief.

   Vinegar eel (Zool.), a minute nematode worm (Leptodera
      oxophila, or Anguillula acetiglutinis), commonly found
      in great numbers in vinegar, sour paste, and other
      fermenting vegetable substances; -- called also vinegar
      worm.

   Vinegar lamp (Chem.), a fanciful name of an apparatus
      designed to oxidize alcohol to acetic acid by means of
      platinum.

   Vinegar plant. See 4th Mother.

   Vinegar tree (Bot.), the stag-horn sumac (Rhus typhina),
      whose acid berries have been used to intensify the
      sourness of vinegar.

   Wood vinegar. See under Wood.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Eel \Eel\, n. [AS. ?l; akin to D., G., & Dan. aal, Icel. [=a]ll,
   Sw. [*a]l.] (Zo["o]l.)
   An elongated fish of many genera and species. The common eels
   of Europe and America belong to the genus Anguilla. The
   electrical eel is a species of Gymnotus. The so called
   vinegar eel is a minute nematode worm. See Conger eel,
   Electric eel, and Gymnotus.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vinegar eel
    n 1: minute eelworm that feeds on organisms that cause
         fermentation in e.g. vinegar [syn: vinegar eel, vinegar
         worm, Anguillula aceti, Turbatrix aceti]