CO picking up beret with one clenched hand (8)
I believe the answer is:
pacifist
'co picking' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'up beret with one clenched hand' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'beret' becomes 'cap' (beret is a type of cap).
'with' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'clenched hand' becomes 'fist' (I've seen this before).
'cap' reversed gives 'pac'.
'pac'+'i'+'fist'='PACIFIST'
Can you help me to learn more?
(Other definitions for pacifist that I've seen before include "One refusing military service" , "One opposes violence and refuses to take part in war" , "non-belligerent" , "War opponent" , "Anti-war person, believes in peaceful settlements" .)