Diagram may show daily temperature (5)
I believe the answer is:
chart
'diagram' is the definition.
(I know that chart is a type of diagram)
'daily temperature' is the wordplay.
'daily' becomes 'char' (both can mean a cleaner).
'temperature' becomes 't' (abbreviation).
'char'+'t'='CHART'
'may show' is the link.
(Other definitions for chart that I've seen before include "Navigational map" , "Hit parade" , "what could be a pie" , "Nautical map" , "series of plots?" .)