This is a reference for kun'yomi homophones in Japanese: words that have the same reading, but slightly different kanji and meanings. While the Internet can be a good place to look up questions about kun'yomi homophones, sometimes it takes longer to find an answer online than it does with one, solid resource (especially if you're new to Japanese and you aren't comfortable typing it yet).
The Kodansha Kanji Usage Guide helps beginners understand the differences in meaning and usage for words that seem to be the same thing at first glance. Set up in English alphabetical order, this small book lists words by their readings. Each reading then has all possible spellings (with kanji) and definitions to help you learn the differences.
This book is especially helpful for beginners learning kanji and focusing more on verbs. There are tons of verb homophones in Japanese and being able to tell the difference between all three のぼるs can be a huge help.
For more, check out our review.