Singular pants

I remember reading somewhere that the word 'pea' is a comparatively recent introduction. We used to call it a 'pease'. Now Marks and Spencer, and presumably other shops, seem to be doing the same for the word 'shorts' and 'pants'. You can now buy a 'short' and a 'pant'. I don't think you can buy a trouser yet, though.

As this swing ticket says: 'This lightweight trekking pant is made from...'. But it goes on: '...so they work in any terrain'. Obviously still a work in progress, this transition.

Odd thing is, on the website it/they is/are called trousers.