机动 jīdòng locomotive
locomotive; motorized; power-driven; adaptable; flexible (use, treatment, timing etc)
How to remember 机动: 机 machine + 动 move = locomotive.
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How it is used
- Two senses: 'motorized' - 机动车 (jīdòngchē) motor vehicle; and 'flexible' - 机动处理 (jīdòng chǔlǐ) to handle flexibly.
- The 'flexible/adaptable' use covers reserve resources: 机动人员 (jīdòng rényuán) a flotating/reserve staff.
- Context tells you between 'engine-powered' and 'kept adaptable'.