The Dictionary of Fashion History by Valerie Cumming, C W and P E Cunnington published by Berg (an imprint of Oxford International Publishers Ltd). This is a revised and updated version of the latter two authors dictionary.
(When I saw the cover image of the Victorian, red and yellow corset, close to, one of my future (but unknown) characters flitted by wearing it...)
Now admittedly I do have quite a few books on historical costume on my bookshelves, some are general, other specific to certain time periods such as the 18th or 19th century. But they each have elements that the others don't.
The newer books have beautiful coloured illustrations, which allow you to see detail, while the much older books relied on old illustrations and black and white images to accompany the text. But old copies of books by Phillis and her husband can be very expensive second hand- and I've picked up a couple in charity shops, but still had to pay quite a bit for them.
The updated dictionary gives a general date period, and a description of the garment, sometimes even a relevent quote. I like the mid-19thC term Howling bags, a slang term for trousers which sport a very 'loud' pattern. I've seen some modern trousers that would certainly fit that description!
If you've ever wanted to know what a particular fabric looked like, or what fibres it was made from, then there's an A-Z covering 50 sides; a glossary of laces- again with dates and descriptions, and a page of obsolete colour names.
Now I don't think anyone would question why the (16th C) Yellowish-green Goose-turd became an obsolete colour...
There's a comprehensive Bibliography too- and I do have a few of the books mentioned.
As many of my characters inhabit the 18th and 19th centuries, I can visualize their clothes better and appreciate the effect on their movements, as well as the texture.
In my Dorset novel my heroine sometimes has to wear clothes that are completely different to her normal attire, and I know that when she first puts them on it will feel strange to her...
Ideally I'd go and look at costumes on display, but costume museums are few and quite a distance from me, and won't necessarily have garments from the time period I need. So books, the web and costume postcards are very useful.
If I chose a particular costume item I'd like for using now, it would be a Calash- especially when I've been to the hairdressers and the weather is breezy... :-)
From any century, what item of clothing, footwear or headgear would you choose?