Ornate gold twist, doubly firm (6)
I believe the answer is:
rococo
'ornate' is the definition.
(I've seen this in another clue)
'gold twist doubly firm' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'twist' says the letters should be written in reverse (I've seen 'twisting' mean this (letters twist back)).
'doubly' shows that letters should be duplicated.
'firm' becomes 'co' (a firm is a company).
'or' back-to-front is 'ro'.
'co' duplicated is 'coco'.
'ro'+'coco'='ROCOCO'
(Other definitions for rococo that I've seen before include "Elaborately ornate" , "Ornate style of decoration." , "Ornamental style associated with Louis XV" , "Delicate architectural style from 18th-century France" , "More elaborate form of baroque" .)