Stayed pronouncedly sober (5)
I believe the answer is:
staid
'sober' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for staid that I've seen before include "Sedate, unadventurous" , "Calm, respectable and unadventurous" , "Sedate, sober" , "Settled" , "Stuffy, traditional" .)