This is something that has confused me for a while. I am no Japanese student, but I do shotokan karate. We are often told to get into a "ready" stance by the sensei using the command "yoi". Wikipedia seems to treat "yoi" as used in the context as interchangeable with shizentai (natural stance). Most karate sites do also translate the meaning as "ready". However, when I try to find the appropriate kanji, the only "yoi" I find is 良, which (as far as I can tell) means good, but has no translation equivalent to "ready" in English. Is the command as used in karate represented by a different kanji or does this same kanji have that meaning in some contexts?
The correct word for it is yōi (用意), but perhaps you failed to perceive vowel length and/or your sensei isn't a native speaker.
In many martial arts we start a match with:
Or in track race:
位置について――用意――ドン！ On your mark......Get set......(bang!)