Three learners maintaining university is quiet (4)
I believe the answer is:
lull
'quiet' is the definition.
(I know that quiet can be written as lull)
'three learners maintaining university' is the wordplay.
'three learners' can mean three substitutions for 'learner'.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'maintaining' indicates putting letters inside (inserted letters are held or maintained).
'university' becomes 'U' (abbreviation for university).
'l'+'l'+'l'='lll'
'lll' enclosing 'u' is 'LULL'.
'is' acts as a link.
(Other definitions for lull that I've seen before include "Make calm" , "Period of inactivity" , "Short spell of calm" , "Peaceful interlude" , "Subside" .)