Round, plump and purple (7)
I believe the answer is:
orotund
'purple' is the definition.
(both can describe florid or pompous writing)
'round plump' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'plump' becomes 'rotund' (I've seen this before).
'o'+'rotund'='OROTUND'
'and' acts as a link.
(Other definitions for orotund that I've seen before include "Sonorous; pompous" , "Of speech, pompous and imposing" , "Not dour (anag.)" , "Pompous (in style)" , "booming" .)