快
カイ, こころよ.い, よし

cheerful, pleasant, agreeable, comfortable

JLPT2 G5 S7 F1074

As per 夬# (scoop out) + 心 heart/emotions → *pleasant*; *comfortable* (← heart with all the unpleasantness scooped out of it) → *refreshing*; *enjoyable*. Compare 欠/缺.

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