Tells about unpunctual son (7)
I believe the answer is:
relates
'tells' is the definition.
(relating is a kind of telling)
'about unpunctual son' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'unpunctual' becomes 'late' (similar in meaning).
'son' becomes 's' (genealogical abbreviation for son).
're'+'late'+'s'='RELATES'
(Other definitions for relates that I've seen before include "Tells (a tale)" , "Narrates" , "Describes" , "couples" .)