Understood diplomacy around yours truly (5)
I believe the answer is:
tacit
'understood' is the definition.
(I know that understood can be written as tacit)
'diplomacy around yours truly' is the wordplay.
'diplomacy' becomes 'tact' (tact can mean diplomacy or sensitivity).
'around' indicates putting letters inside.
'yours truly' becomes 'I' (the person who set this crossword).
'tact' enclosing 'i' is 'TACIT'.
(Other definitions for tacit that I've seen before include "Implicit, unspoken" , "Understood, implicit" , "Implicitly understood" , "Respect, admiration" , "Wordless" .)