Learner in university river, tranquil (4)
I believe the answer is:
calm
'tranquil' is the definition.
(synonyms)
'learner in university river' is the wordplay.
I cannot really understand how this works, but
'learner' could be 'l' (as in a learner driver with L-plates on their car) and 'l' is found in the answer.
'river' could be 'cam' (river in Cambridge, England) and 'cam' is located in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for calm that I've seen before include "Self-possessed" , "Serene" , "Peace or stillness" , "Peaceful, undisturbed" , "Composed and collected" .)