Glossy took part in protest with youth leader (6)
I believe the answer is:
satiny
'glossy' is the definition.
(synonyms)
'took part in protest with youth leader' is the wordplay.
I cannot quite see how this works, but
'took' could be 'sat' (sit can mean to take an exam) and 'sat' is located in the answer.
'part' could be 'in' (synonyms) and 'in' is found within the answer.
'youth' could be 'y' and 'y' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for satiny that I've seen before include "having a smooth, gleaming surface" , "shiny and lustrous" , "Smooth and glossy" , "smooth result?" , "Silkily smooth" .)