not (one's) department(redirected from not his department)
not (one's) department
Not one's area of expertise or responsibility. I can't approve expense reports—that's not my department. Car repair isn't really Jim's department, but I'll take a look at the engine if you like.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
not your department
If a task or area of knowledge is not your department, you are not responsible for it or do not know much about it. The political issues are something else, but that's not really my department. `If you identify him, then what?' — `Not my department.' Note: You can also say that something is your department if you are responsible for it or know a lot about it. `So what do we do with him?' Admiral Polaski asked. `That, gentlemen, is our department,' Rintner said. Bill spoke expertly. This had been his department.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012