SI unit of substance in gold and uranium alloy (6)
I believe the answer is:
ormolu
'alloy' is the definition.
(ormolu is a kind of alloy)
'si unit of substance in gold and uranium' is the wordplay.
I cannot quite understand how this works, but
'unit' could be 'mol' (mol is a kind of unit) and 'mol' is present in the answer.
'of' could be 'o' and 'o' is found within the answer.
'substance' could be 'ru' (Ru is an example) and 'ru' is found within the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ormolu that I've seen before include "Alloy of copper and zinc" , "Brass that looks like gold" , "Gilded metallic ware" , "Alloy for gilding" , "Gold-coloured alloy used to decorate furniture" .)