The Collaborative International Dictionary of English v.0.48:

Annex \An*nex"\, v. t. [imp. & p. p. Annexed; p. pr. & vb. n.
   Annexing.] [F. annexer, fr. L. annexus, p. p. of annectere
   to tie or bind to; ad + nectere to tie, to fasten together,
   akin to Skr. nah to bind.]
   1. To join or attach; usually to subjoin; to affix; to
      append; -- followed by to. "He annexed a codicil to a
      will." --Johnson.
      [1913 Webster]

   2. To join or add, as a smaller thing to a greater.
      [1913 Webster]

            He annexed a province to his kingdom. --Johnson.
      [1913 Webster]

   3. To attach or connect, as a consequence, condition, etc.;
      as, to annex a penalty to a prohibition, or punishment to
      guilt.
      [1913 Webster]

   Syn: To add; append; affix; unite; coalesce. See Add.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Annex \An*nex"\, v. i.
   To join; to be united. --Tooke.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Annex \An*nex"\, n. [F. annexe, L. annexus, neut. annexum, p. p.
   of annectere.]
   Something annexed or appended; as, an additional stipulation
   to a writing, a subsidiary building to a main building; a
   wing.
   [1913 Webster]

WordNet (r) 3.0 (2006):

annex
    n 1: an addition that extends a main building [syn: annex,
         annexe, extension, wing]
    v 1: take (territory) as if by conquest; "Hitler annexed
         Lithuania"
    2: attach to

Moby Thesaurus II by Grady Ward, 1.0:

177 Moby Thesaurus words for "annex":
   L, abstract, accession, accessory, accompaniment, accroach,
   acquire, add, addenda, addendum, additament, addition, additive,
   additory, additum, adjoin, adjunct, adjuvant, affix, agglutinate,
   anchor, and, annexation, appanage, append, appendage, appendant,
   appropriate, appurtenance, appurtenant, arm, arrogate, associate,
   attach, attachment, augment, augmentation, bag, belay, block,
   boost, borrow, burden, cabbage, cement, cinch, clamp, clinch, coda,
   collar, collectivize, commandeer, communalize, communize,
   complement, complicate, concomitant, confiscate, conjoin, connect,
   continuation, cop, corollary, cramp, crib, decorate, defraud,
   distrain, ell, embezzle, encumber, engraft, expropriate, extension,
   extort, extrapolation, fasten, filch, fix, fixture, gain, garnish,
   get at, get hold of, glom on to, glue on, grab, graft, grapple,
   have, hitch on, hook, impound, impress, increase, increment, infix,
   join, join with, knit, land, lay hands on, levy, lift, link,
   make fast, make off with, moor, nationalize, nip, obtain, offshoot,
   ornament, palm, paste on, pendant, pick up, pilfer, pinch, plus,
   poach, postfix, preempt, prefix, press, procure, purloin, put to,
   put with, reinforcement, replevin, replevy, run away with, rustle,
   saddle with, screw up, scrounge, secure, seize, sequester,
   sequestrate, set, set to, shoplift, side effect, side issue,
   slap on, snare, snatch, snitch, socialize, steal, subjoin, suffix,
   superadd, superpose, supplement, swindle, swipe, tack on, tag,
   tag on, tailpiece, take, take on, take over, take possession,
   take up, thieve, tighten, trice up, trim, undergirding, unite,
   unite with, walk off with, wing