Pericles dancing with son is very amusing (9)
I believe the answer is:
priceless
'very amusing' is the definition.
(I've seen this before)
'pericles dancing with son' is the wordplay.
'dancing with' indicates anagramming the letters.
'son' becomes 's' (genealogical abbreviation for son).
'pericles' mixed up with 's' makes 'PRICELESS'.
'is' acts as a link.
(Other definitions for priceless that I've seen before include "Untagged" , "Rich" , "Of incalculable value" , "Very precious; highly amusing" , "Of inestimable value" .)