A line about a paragon (5)
I believe the answer is:
pearl
'paragon' is the definition.
(I've seen this before)
'a line about a' is the wordplay.
'a' becomes 'per'.
'line' becomes 'l'.
'about' is an insertion indicator.
'per'+'l'='perl'
'perl' going around 'a' is 'PEARL'.
(Other definitions for pearl that I've seen before include "Drop" , "Lustrous structure in a mollusc shell" , "Gem; an attacked Harbor" , "Precious gem" , "White - jewel" .)