I was recently reading the Intelligent Life magazine (more praise of it later) and stumbled upon this paragraph in an article by Rebecca Willis:
‘Back in the days when I wrote about hotels for a living, the man I was eventually to marry sometimes joined me on my travels. And a curious thing would happen as we crossed the latest hip-hotel lobby: a thought would flash across my mind – ‘what a hideous lamp’, for instance – and a micro-second later he would say: ‘I love that lamp, I wonder where it’s from?’ It could be a sofa, a painting, a fabric, a paint colour: whatever, I soon learnt to wait for the inverse echo of my reaction. It was the first inkling that we might not be totally compatible in the taste department‘ (note the typical British understatement).
I was very excited by this peculiar use of the word ‘department’, only to hear it again a week later. I was chatting to to a colleague about the advantages and disadvantages of being a tall woman, and she wisely remarked that ‘the pickings in the men’s department are rather slim for the ladies who happen to be quite tall‘ (I’ll have to agree on this one). So it turned out that you can use the word department rather freely in contexts like these.
MacMillan Dictionary also suggests that you can use the word department to talk about something you know well or something you’re responsible for, for instance ‘The gardening is Simon’s department.’