'费劲' (fèi jìn) literally combines '费' (fèi), meaning 'to expend' or 'to cost', and '劲' (jìn), meaning 'effort', 'strength', or 'energy'. Together, it describes an action or situation that requires considerable physical or mental effort — something that is strenuous, laborious, or hard to accomplish. It often implies difficulty beyond ordinary exertion, carrying a slight tone of frustration or weariness.

This word is commonly used in everyday spoken and written Chinese to describe tasks like lifting heavy objects, solving complex problems, persuading someone stubborn, or even learning a difficult skill. It functions flexibly as both an adjective ('This task is exhausting') and a verb ('It took me ages to finish — I really had to exert myself'). Unlike formal synonyms, 费劲 is neutral-to-informal and frequently appears in conversational contexts, especially when expressing mild complaint or empathetic acknowledgment of difficulty.