Only recently I discovered this great website: Japanese Garden Dictionary: A Glossary for Japanese Gardens and Their History by Ono Kenkichi and Walter Edwards.
This is absolutely great. There are plenty of, say Japanese word-lists available on the web that may or may not have a focus on gardens. Only few of these include Kanji and Kana writing. This site looks very, very complete, lean and mean, hence it is also very fast.
There is one other Dictionary on the web, that I know of, that can compete with it and that is JAANUS, the on-line Dictionary of Japanese Architectural and Art Historical Terminology compiled by Dr. Mary Neighbour Parent, that for long has been listed on our Links page under III – Sites that address related topics. This latter one covers a much broader subject and also includes many photo’s.
There are however a number of specific garden related words that are not defined in JAANUS and that can be found in the nabunken.go.jp database.
P.s: I have now added the Links page where these will be permanently listed.