Rum spilt by a learner on the wall! (5)
I believe the answer is:
mural
'wall' is the definition.
'rum spilt by a learner on' is the wordplay.
'spilt' is an anagram indicator.
'by' means one lot of letters go next to another.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'on' says to put letters next to each other.
'rum' is an anagram of 'mur'.
'mur'+'a'+'l'='MURAL'
'the' is the link.
(Other definitions for mural that I've seen before include "Wall design" , "Large wall painting" , "Wall art" , "Drawing on a wall" , "Wall-painting" .)