Kanji-to-English dictionaries can be devilishly difficult to use. Imagine your bus is stuck in Tokyo traffic and you see a road sign reading "徐行." You whip out your passport-size electronic kanji dictionary.
You learned the second character, 行 ("go"), early on. The other, 徐, is totally unfamiliar to you.
If you knew a Japanese pronunciation for 徐, your task would be easy: Virtually every kanji dictionary--be it in electronic or book form, or online--includes a pronunciation-based character index. But what can you do when you do not know a pronunciation of an unfamiliar kanji?
You could consult a stroke-count index. These are sometimes included in paperback kanji handbooks and electronic kanji dictionaries. It is easy to make a mistake counting the number of strokes, though, and combing through column after column for a character can be time-consuming and frustrating.
Most kanji dictionaries--both those designed for foreigners and those for native speakers--arrange characters according to a system of 214 character components called "radicals" (部首 bushu, "section heads"). Some radicals are actual kanji (such as 耳 "ear," 白 "white," and 車 "vehicle," for example) and their variants ( for 水 "water" and for 手 "hand" for example). Others-- such as "roof," and "illness"--never appear as independent characters.
Even native kanji sleuths may have difficulty maneuvering through the traditional radical system in a kanji dictionary for native speakers (漢和辞典, kanwajiten). One vexing problem is that most characters contain from two to eight radicals, and a dictionary user does not always identify the correct one.
For example, you might also have spotted 積載量 (sekisairyou, "load capacity") on the truck idling beside your bus. The third character, 量, includes three radicals: 日("sun"), 一 ("one"), and 里 ("village"). The "correct" radical is usually the component of the kanji most closely associated with its overall meaning. This presents you with the conundrum of needing to know the meaning of 量 in order to look up its meaning ! Hmmm...
You type 日 into your electronic dictionary. Oops, wrong! The correct classifier happens to be 里.
Several creators of user-friendly dictionaries for foreigners have devised innovative alternatives. The first of these trailblazers was Andrew Nelson. Until 1990, Nelson's "Modern Reader's Japanese-English Character Dictionary" (Tuttle, 1962) was the only comprehensive modern kanji-to-English dictionary available, having virtually replaced Rose-Innes' classic prewar work.
Nelson retained use of the radicals while creating some new, practical rules for determining under which radical a character would be listed. He also listed many characters under their "incorrect" (easily mistaken) radicals, as well as their correct ones.
Advances in computer lexicography have now made even more useful kanji look-up tools available to us. John Haig, in "The New Nelson Japanese-English Character Dictionary," (Tuttle, 1997), replaced Nelson's look-up system with the Universal Radical Index: In Haig's system, a character can be found under any known radical within it.
Jim Breen's popular and incredibly extensive online kanji dictionary, (accessible at links) is similarly user-friendly: Using his MultiRadical Method, you simply click on several radicals, and the desired character containing them all will magically pop up.
Jack Halpern's "New Japanese-English Character Dictionary" (Kenkyusha, 1990), and its portable version, "The Kanji Learner's Dictionary," (Kodansha, 1999) both utilize his revolutionary System of Kanji Indexing by Patterns. SKIP classifies characters into four easy-to-identify geometrical patterns--left-right, up-down, enclosure, and solid--generally making it a snap to find your desired kanji even if you are unfamiliar with radicals.
Spahn and Hadamitzky's "The Kanji Dictionary" (Tuttle, 1996), lists compound words under each of the characters that make up a word, instead of only under its first character. For example, you can avoid altogether having to search for the unknown 徐 in order to locate 徐行, because it will also be listed under 行-- whose pronunciation you already know.
Taking full advantage of new search tools like these will make tracking down an unfamiliar kanji less and less like searching for a pebble in a 20-kg bag of rice.
Oh, yes, 徐行 (jokou) means "go slowly".
Before you plunk down your hard-earned cash for a kanji dictionary, why not read more about them ?