A step in the design of costume jewellery (5)
I believe the answer is:
paste
'design of costume jewellery' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'a step in' is the wordplay.
'a step' can be anagrammed to 'PASTE'.
However, I am unsure how the anagram is indicated.
'the' acts as a link.
Can you help me to learn more?
(Other definitions for paste that I've seen before include "Watery adhesive" , "Tapes (anag.)" , "Thoroughly beat" , "It is used to stick wallpaper" , "One way to fix" .)