Diagram, I see, is explicit (7)
I believe the answer is:
graphic
'explicit' is the definition.
(similar in meaning)
'diagram i see' is the wordplay.
'diagram' becomes 'graph' (graphing is a kind of diagraming).
'see' becomes 'C' (the word for the letter, according to Chambers).
'graph'+'i'+'c'='GRAPHIC'
'is' is the link.
(Other definitions for graphic that I've seen before include "(Of an account) vivid" , "Of drawing or lettering - vivid" , "Relating to visual art; explicit" , "Visually clearly described" , "Described in detail" .)