Particle of meat, not dry (4)

'particle' is the definition.
(muon is a kind of particle)

'of meat not dry' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is found within the answer.
'not' could be 'un' (prefix meaning 'not') and 'un' is present in the remaining letters.
A single letter 'm' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?