Meaning of 'EM in English

'EM

/ əm; NAmE / pronoun

( informal ) = them :

Don't let 'em get away.

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WORD ORIGIN

Middle English : originally a form of hem , dative and accusative third person plural pronoun in Middle English ; now regarded as an abbreviation of them .

Oxford Advanced Learner's English Dictionary.      Оксфордский английский словарь для изучающик язык на продвинутом уровне.