Flamboyant jumper worn by choice, oddly (6)
I believe the answer is:
rococo
'flamboyant' is the definition.
(thesaurus)
'jumper worn by choice oddly' is the wordplay.
'jumper' becomes 'roo' (short for kangaroo, something which jumps).
'worn by' means one lot of letters goes inside another (I've seen this in other clues).
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
The alternate letters of 'choice' are 'coc'.
'roo' going around 'coc' is 'ROCOCO'.
(Other definitions for rococo that I've seen before include "Eighteenth-century French architectural style" , "More elaborate form of baroque" , "Fanciful decoration" , "Ornate style of decoration." , "Elaborate baroque style of ornamentation" .)