Until the 17th century, dictionaries were meaning based and not alphabetized. Is there such a meaning based dictionary available today? I did a quick google search and failed to find one.

According to lexicology, there are two kinds of dictionaries: onomasiological (name-oriented, alphabetized lexicons) and semasiological (meaning-oriented, thesuaruses). Two good books on lexicology are: (1) Ladislav Zgusta (1971) Manual of lexicography (academic) and (2) Sidney Landau (2001) Dictionaries: The Art and Craft of Lexicography (non-academic).

Thanks for your help. I'm getting ready to do a teacher inservice on meaning-based spelling and wanted to share alternatives to the dictionaries available in their classrooms.

You're welcome. There's also two other books I just thought of: Jonathon Green, a British academic lexicographer, wrote Chasing The Sun: Dictionary-Makers and the Dictionaries They Made in 1996, and Charles Read's (1986) Children's Creative Spelling. I haven't read the last book, yet, but I can vouch that others a great reads.