Japanese for big. Here is the kanji:
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The character is a pictograph of a person standing with arms and legs spread out to look as large as possible. In addition to being pronounced ookii (as a standalone word), it can be pronounced tai, dai, or oo (as the o sound in home only longer) when used in combination with other characters.
Used in combination this character forms words like: taikai (assembly), daigaku (university), and oogoe (loud voice).