To make someone work very hard; to boss someone around or exploit someone by overworking them (pejorative).
彼は部下を毎日こき使って休ませない。
He works his subordinates hard every day and doesn't let them rest.
若い頃、親にこき使われて辛かったと話していた。
She said that when she was young she was worked hard by her parents and it was tough.
人をこき使う上司の下では働きたくない。
I don't want to work under a boss who pushes people around.
こき使われたアルバイトはやめてしまった。
The part-timer who was overworked quit.