What with overwork and little sleep at night, he fell ill.
500
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働く, はたらく
1. to work, to labor, to labour
2. to function, to operate, to be effective, to work (i.e. ... works), to come into play
3. to commit (e.g. a crime), to perpetrate, to do, to act, to practise, to practice
4. to be conjugated