引用自大家论坛,说的挺全面的：
retain作"雇佣"讲时,仅指对lawyer,specialist等专门人才的雇用
retain:(LEGAL)to obtain the services of a lawyer by paying them in advance
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retain,employ,get,obtain
shared menaing:having the service of a lawyer
to retain a lawyer -- a fee is paid in advance
to employ a lawyer -- a salary is paid to the lawyer (as a regular employee)
to hire a lawyer -- reimbursement structure unclear
to get/obtain a lawyer -- fee structure isn't the main emphasis