It's easy to implement user-specified synonyms with a custom Analyzer. All you have to do is to map tokens to a synonym with a hash table. You can find some information on how to implement your own Analyzer in the mailing list archives.
Lucy's SnowballStopFilter already supports custom stoplists and could be leveraged to map synonyms with just a few changes. What do the Lucy developers think about supporting synonyms in core? Nick
