The Collaborative International Dictionary of English v.0.48:

Etymon \Et"y*mon\, n.; pl. E. Etymons, Gr. Etyma. [L., fr.
   Gr. 'e`tymon the true literal sense of a word according to
   its derivation, an etymon, fr. ? true, real, prob, akin to
   Skr. sotya, E. sooth. See Sooth.]
   1. An original form; primitive word; root.
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   2. Original or fundamental signification. [R.]
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            Given as the etymon or genuine sense of the word.
                                                  --Coleridge.
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WordNet (r) 3.0 (2006):

etymon
    n 1: a simple form inferred as the common basis from which
         related words in several languages can be derived by
         linguistic processes [syn: etymon, root]