Characters in Cognito gobsmacked by what's in Africa (4)

I believe the answer is:

toga

I'm a little stuck... Click here to teach me more about this clue!

'africa' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for toga that I've seen before include "Graph's y value" , "garment of old" , "Roman gents' cloak" , "Ancient Roman garment" , "Roman clothing" .)

I've seen this clue in the Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.