Paint brush finally adapted into a device holding pillbox in place (6)
I believe the answer is:
hatpin
'a device holding pillbox in place' is the definition.
I can't judge whether this definition defines the answer.
'paint brush finally adapted' is the wordplay.
'finally' suggests the final letters.
'adapted' indicates an anagram.
The last letter of 'brush' is 'h'.
'paint'+'h'='painth'
'painth' anagrammed gives 'HATPIN'.
'into' is the link.
Can you help me to learn more?
(Other definitions for hatpin that I've seen before include "Bonnet fixer" , "Headgear fixer" , "Fastener for headgear" , "Fastener for millinery" .)