Tell about being unpunctual (6)
I believe the answer is:
relate
'tell' is the definition.
(as in to tell or relate a story)
'about being unpunctual' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'being unpunctual' becomes 'late' (similar in meaning).
're'+'late'='RELATE'
(Other definitions for relate that I've seen before include "link" , "Tell; a counselling service" , "Narrate or associate" , "Tell - the marriage guidance people" , "Recount" .)