On top of (4)
'on top of' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for upon that I've seen before include "On tope of" , "At a prescribed point in time" , "Straddling" , "Onto" , "Au courant" .)
'on top of' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for above that I've seen before include "Aforementioned" , "At a higher level" , "Given earlier (in text)" , "Mentioned earlier" , "Superior to" .)