American tree by which nursery rhyme is started (7)

I believe the answer is:

hickory

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

'american tree' is the definition.
'hickory' can be an answer for 'tree' (hickory is a kind of tree). I'm unsure of the 'american' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for hickory that I've seen before include "Hard wood" , "Heavy wood" , "Nut tree" , "North American tree" .)

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.