First stop: a dictionary everybody should know about, though few do: Hobson-Jobson: a glossary of colloquial Anglo-Indian words and phrases, first published in the 1880s. If I do a search for 'curry' here's what I get
And of course we need to visit the OED for its [literary] perspective. (and I'll add the word tiffin to your vocabulary too)
Another site that I think of as pretty useful is Penzey's Spices
The bottom line: 'curry' isn't one thing, but a cover term for a kaleidoscope of mixtures of various spices. A glorious subject. How to get a handle on it? A few sites that sketch something of the complexities:
Prepare Curry Paste and Powder for Asian Cuisines"Curry is not a thing, it is a state of being"
Spice Library from Spices Board India
Indian Spices from The Cook's Thesaurus
...and here's what Amazon gives me for the searches curry spices (5000+) and "curry spices" (133)