Ruffle Jack on the subject of missing uranium (5)
I believe the answer is:
jabot
'ruffle' is the definition.
(jabot is a kind of ruffle)
'jack on the subject of missing uranium' is the wordplay.
'jack' becomes 'j' (playing card abbreviation).
'on the subject of' becomes 'about' (I've seen this before).
'missing' suggests deleting specific letters.
'uranium' becomes 'u' (U is the chemical symbol for uranium).
'about' with 'u' removed is 'abot'.
'j'+'abot'='JABOT'
(Other definitions for jabot that I've seen before include "Ruffle over shirt-front" , "Lace frill" , "bit of Highland dress" .)