The Collaborative International Dictionary of English v.0.48:

Vanilla \Va*nil"la\, n. [NL., fr. Sp. vainilla, dim. of Sp.
   vaina a sheath, a pod, L. vagina; because its grains, or
   seeds, are contained in little pods.]
   [1913 Webster]
   1. (Bot.) A genus of climbing orchidaceous plants, natives of
      tropical America.
      [1913 Webster]

   2. The long podlike capsules of Vanilla planifolia, and
      Vanilla claviculata, remarkable for their delicate and
      agreeable odor, for the volatile, odoriferous oil
      extracted from them; also, the flavoring extract made from
      the capsules, extensively used in confectionery,
      perfumery, etc.
      [1913 Webster]

   Note: As a medicine, vanilla is supposed to possess powers
         analogous to valerian, while, at the same time, it is
         far more grateful.
         [1913 Webster]

   Cuban vanilla, a sweet-scented West Indian composite shrub
      (Eupatorium Dalea).

   Vanilla bean, the long capsule of the vanilla plant.

   Vanilla grass. Same as Holy grass, under Holy.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vanilla
    adj 1: flavored with vanilla extract; "he liked vanilla ice
           cream"
    2: plain and without any extras or adornments; "the most common
       type of bond is the straight or plain vanilla bond"; "the
       basic car is known as the vanilla version"
    n 1: any of numerous climbing plants of the genus Vanilla having
         fleshy leaves and clusters of large waxy highly fragrant
         white or green or topaz flowers
    2: a flavoring prepared from vanilla beans macerated in alcohol
       (or imitating vanilla beans) [syn: vanilla, vanilla
       extract]
    3: a distinctive fragrant flavor characteristic of vanilla beans

The Jargon File (version 4.4.7, 29 Dec 2003):

vanilla
 adj.

    [from the default flavor of ice cream in the U.S.] Ordinary flavor,
    standard. When used of food, very often does not mean that the food is
    flavored with vanilla extract! For example, vanilla wonton soup means
    ordinary wonton soup, as opposed to hot-and-sour wonton soup. Applied to
    hardware and software, as in ?Vanilla Version 7 Unix can't run on a vanilla
    11/34.? Also used to orthogonalize chip nomenclature; for instance, a 74V00
    means what TI calls a 7400, as distinct from a 74LS00, etc. This word
    differs from canonical in that the latter means ?default?, whereas
    vanilla simply means ?ordinary?. For example, when hackers go on a 
    great-wall, hot-and-sour soup is the canonical soup to get (because that
    is what most of them usually order) even though it isn't the vanilla
    (wonton) soup.


The Free On-line Dictionary of Computing (30 December 2018):

vanilla

   1. (Default flavour of ice cream in the US) Ordinary
   flavour, standard.  When used of food, very often does not
   mean that the food is flavoured with vanilla extract!  For
   example, "vanilla wonton soup" means ordinary wonton soup, as
   opposed to hot-and-sour wonton soup.  Applied to hardware and
   software, as in "Vanilla Version 7 Unix can't run on a
   vanilla PDP 11/34."  Also used to orthogonalise chip
   nomenclature; for instance, a 74V00 means what TI calls a
   7400, as distinct from a 74LS00, etc.  This word differs from
   canonical in that the latter means "default", whereas
   vanilla simply means "ordinary".  For example, when hackers go
   to a chinese restaurant, hot-and-sour wonton soup is the
   canonical wonton soup to get (because that is what most of
   them usually order) even though it isn't the vanilla wonton
   soup.

   [Jargon File]

   (1994-11-04)

   2. Snobol4 by Catspaw, Inc. for MS-DOS.

   (ftp://cs.arizona.edu/snobol4/vanilla.arc).

   (1992-02-05)