Slow down in river when treacle stirred in? (10)
I believe the answer is:
decelerate
'slow down' is the definition.
(synonyms)
'river when treacle stirred in?' is the wordplay.
'river when' becomes 'dee' (I am not sure about this - if you are sure you should believe this answer much more).
'stirred' indicates an anagram.
'in?' means one lot of letters goes inside another.
'treacle' is an anagram of 'celerat'.
'dee' placed around 'celerat' is 'DECELERATE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for decelerate that I've seen before include "ease up" , "Slow down" , "Reduce speed" , "Move more slowly" .)