Answer: The most refined versions of the "language of flowers" date back to Victorian times and tussie-mussies and over the years and depending on who you ask it seems that the meanings may shift around a bit. Here are several versions for you to consider.
The first seems fairly representative of modern day interpretations http://members.xoom.com/mangey/interesting_stuff.htm and it lists lavender for "acknowledgement";
the second is from a wedding related business
http://www.weddingpetals.com/languageofflowers.html and it lists lavender for "devotion";
this last is reprinted from Collier's Cyclopedia of Commercial and Social Information and Treasury of
Useful and Entertaining Knowledge, compiled by Nugent Robinson. P.F. Collier, 1882 http://www.apocalypse.org/pub/u/hilda/flang.html and it lists lavender for "distrust".
So you see, the meanings depend on who you ask and possibly how firmly you believe in this somewhat contrived language -- there really isn't a hard and fast answer to your question.
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