The Collaborative International Dictionary of English v.0.48:

Brittle \Brit"tle\, a. [OE. britel, brutel, AS. bryttian to
   dispense, fr. bre['o]tan to break; akin to Icel. brytja, Sw.
   bryta, Dan. bryde. Cf. Brickle.]
   Easily broken; apt to break; fragile; not tough or tenacious.
   [1913 Webster]

         Farewell, thou pretty, brittle piece
         Of fine-cut crystal.                     --Cotton.
   [1913 Webster]

   Brittle silver ore, the mineral stephanite.
      [1913 Webster]

WordNet (r) 3.0 (2006):

brittle
    adj 1: having little elasticity; hence easily cracked or
           fractured or snapped; "brittle bones"; "glass is
           brittle"; "`brickle' and `brickly' are dialectal" [syn:
           brittle, brickle, brickly]
    2: lacking warmth and generosity of spirit; "a brittle and
       calculating woman"
    3: (of metal or glass) not annealed and consequently easily
       cracked or fractured [syn: brittle, unannealed]
    n 1: caramelized sugar cooled in thin sheets [syn: brittle,
         toffee, toffy]

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "brittle":
   atrophied, breakable, brittle as glass, capricious, changeable,
   cheap-jack, cobwebby, corruptible, crackable, crisp, crispy,
   crumbly, crump, crushable, dainty, deciduous, delicate,
   delicately weak, desiccated, dried-up, dying, effeminate,
   emaciated, ephemeral, evanescent, fading, fickle, fissile,
   fleeting, flimsy, flitting, fly-by-night, flying, fracturable,
   fragile, frail, frangible, friable, fugacious, fugitive, gimcrack,
   gimcracky, gossamery, impermanent, impetuous, impulsive,
   inconstant, insecure, insubstantial, jerry, jerry-built, lacerable,
   light, lightweight, momentary, mortal, mutable, namby-pamby,
   nondurable, nonpermanent, papery, parchmenty, passing, pasteboardy,
   perishable, puny, scissile, sensitive, sere, shatterable, shattery,
   shivery, short-lived, shriveled, shrunken, sissified, sleazy,
   slight, splintery, tacky, temporal, temporary, transient,
   transitive, transitory, undurable, unenduring, unstable,
   unsubstantial, volatile, vulnerable, wasted, weak, wilted, wispy,
   withered, wizened, womanish, wrinkled



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

brittle
 adj.

    Said of software that is functional but easily broken by changes in
    operating environment or configuration, or by any minor tweak to the
    software itself. Also, any system that responds inappropriately and
    disastrously to abnormal but expected external stimuli; e.g., a file system
    that is usually totally scrambled by a power failure is said to be brittle.
    This term is often used to describe the results of a research effort that
    were never intended to be robust, but it can be applied to commercial
    software, which (due to closed-source development) displays the quality far
    more often than it ought to. Oppose robust.


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

brittle
fragile

    Said of software that is functional but easily
   broken by changes in operating environment or configuration,
   or by any minor tweak to the software itself.  Also, any
   system that responds inappropriately and disastrously to
   abnormal but expected external stimuli; e.g. a file system
   that is usually totally scrambled by a power failure is said
   to be brittle.  This term is often used to describe the
   results of a research effort that were never intended to be
   robust, but it can be applied to commercially developed
   software, which displays the quality far more often than it
   ought to.

   Opposite of robust.

   [Jargon File]

   (1995-05-09)