Subject of test words that may follow French and precede Latin? (6,3)

I believe the answer is:

guinea pig

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

'subject' is the definition.
(I have seen 'Subject of trial ' mean 'guinea pig' so perhaps 'subject' could also mean 'guinea pig')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for guinea pig that I've seen before include "Pet - subject of experiment" , "Experimented-on animal" , "South American cavy" , "rodent eaten in Peru" , "subject of experimentation" .)

I've seen this clue in The Telegraph.

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.