They work with material, joints and locks (12)
I believe the answer is:
seamstresses
'they work with material' is the definition.
The definition suggests an adverb but the answer is not.
'joints and locks' is the wordplay.
'joints' becomes 'seams' (seam is a kind of joint).
'and' means one lot of letters go next to another.
'locks' becomes 'tresses' (I've seen this before).
'seams'+'tresses'='SEAMSTRESSES'
Can you help me to learn more?
(Another definition for seamstresses that I've seen is " they create?".)