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bad; wrong; naughty
must not (do, be); should not; ought not to
useless; no good; bad
hopeless; beyond hope
unfortunate; a shame; a pity
unable to drink (alcohol)
so as not to ...; so that ... (won't); in case ...; for fear that ...; lest ...
遅刻してはいけないと思います。
I think you shouldn't be late.
無断欠席はいけないことですよ。
Skipping without notice is wrong.
人の悪口を言うのはいけないことだと叱られた。
I was scolded that it's wrong to speak ill of others.