'Saippuakivikauppias' is the world's longest palindrome, a fantastic Finnish word. What does it actually mean though?

It is Finnish for "a dealer in lye", meaning a seller of soap stone.
http://www.guinnessworldrecords.com/world-records/longest-palindromic-word

Saippuakivikauppias is the Finnish word for a soapstone seller.

All the sites I found say 'seller of soap stone' except this one that says "saippuakuppinippukauppias" is a 'soap cup dealer' but I might add it does have 6 more letters than your effort here, therefore this is the longest palindrome.
http://thinkzone.wlonk.com/WordFun/WordFun.htm

'Saippuakivikauppias' is someone who sells caustic soda according to the Guinness Book or World Records and a Finnish translator. I don't know where soap stone came from. Besides, wouldn't the word 'steatite' be included if it were soapstone? Latin names cross these boundaries.

Lye is a strong solution of sodium or potassium hydroxide.
Sodium hydroxide is commonly called called Caustic soda.
Lye is used to make soap.
A lye seller would sell lye to people who would use it to make soap.

I too was puzzled by the "stone" addition.

Here is some more information from peasy's site:
http://thinkzone.wlonk.com/WordFun/WordFun.htm

saippuakauppias - soap dealer
saippurakaruppias - soap salesman
saippuakivikauppias - lye dealer
saippuakuppinippukauppias - soap cup dealer