Surplus EU's saying America is behind (7,7)

I believe the answer is:

gluteus maximus

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

'behind' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?

'surplus eu's saying america' is the wordplay.
'surplus' becomes 'glut' (glut can mean a surplus or surfeit).
'saying' becomes 'maxim' (maxim is a kind of saying).
'america' becomes 'US' (United States).
'glut'+'eus'+'maxim'+'us'='GLUTEUS MAXIMUS'

'is' acts as a link.

Can you help me to learn more?

(Another definition for gluteus maximus that I've seen is " behind in Latin".)

I've seen this clue in The Independent.

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.