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character (esp. kanji); letter; written text
handwriting; penmanship
the ... word (e.g. "the L word" = "love")
「字」 has other readings with different meanings.
書いてある字が小さくて読めません。
I can't read this character.
先生は字がとても綺麗だ。
The teacher has very beautiful handwriting.
字をきれいに書きましょう。
Let's write the characters neatly.