The term 'Purloin Future Sirloin' is a combination of two crossword solutions, 'RUSTLE' and 'Future Sirloin'. RUSTLE is a verb meaning to steal or take something without permission. It is derived from the Old English word 'rustian', which means to make a noise like that of a small animal. Future Sirloin is a cut of beef taken from the upper part of the cow's hindquarters. It is known for its tenderness and flavor. Together, the two words form a phrase that suggests taking something without permission in the future.