"孙公司指的是子公司的子公司，sub作为前缀有在……下面、下位的意思，所以可以用sub-subsidiary 这个词来表达。如：

证券公司应当将所有子公司以及比照子公司管理的各类孙公司纳入全面风险管理体系， 强化分支机构风险管理，实现风险管理全覆盖。全面风险管理体系应当包括可操作的管理制度、健全的组织架构、可靠的信息技术系统、量化的风险指标体系、专业的人才队伍、有效的风险应对机制。

A securities company shall include all its subsidiaries and sub-subsidiaries managed as subsidiaries in the all-round risk management system to enhance the risk management in branches and realize the full coverage of risk management. An all-round risk management system shall cover operable management rules, a sound organizational structure, a reliable information technology system, a quantitative risk index system, a professional talent team and an effective risk response mechanism."