The Collaborative International Dictionary of English v.0.48:

Geminate \Gem"i*nate\, a. [L. geminatus, p. p. of genimare to
   double. See Gemini.] (Bot.)
   In pairs or twains; two together; binate; twin; as, geminate
   flowers. --Gray.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Geminate \Gem"i*nate\, v. t.
   To double. [R.] --B. Jonson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

geminate
    n 1: a doubled or long consonant; "the `n' in `thinness' is a
         geminate"
    v 1: form by reduplication; "The consonant reduplicates after a
         short vowel"; "The morpheme can be reduplicated to
         emphasize the meaning of the word" [syn: reduplicate,
         geminate]
    2: occur in pairs [syn: pair, geminate]
    3: arrange in pairs; "Pair these numbers" [syn: pair,
       geminate]
    4: arrange or combine in pairs; "The consonants are geminated in
       these words"

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "geminate":
   Janus-like, ambidextrous, bifacial, bifold, biform, bilateral,
   binary, binate, biparous, bivalent, conduplicate, copy, disomatous,
   ditto, double, double-faced, dual, dupe, duple, duplex, duplicate,
   geminated, ingeminate, multiply by two, redouble, reduplicate,
   repeat, replicate, reproduce, second, secondary, twin, twinned,
   two-faced, two-level, two-ply, two-sided, two-story, twofold