Crossword Genius

Weight not possibly over two-fifths of a stone? (5)

Ross

I believe the answer is:

tonne

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

'weight' is the definition.
(I've seen this before)

'not possibly over two-fifths of a stone?' is the wordplay.
I cannot really see how this works, but
an anagram of 'not' is 'ton' which is located in the answer.
The remaining letters 'ne' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for tonne that I've seen before include "One thousand kilograms" , "Heavyweight" , "Great weight" , "Metric weight unit" , "1,000 kg" .)

I've seen this clue in the Evening Standard.
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.