Therefore expresses refusal when given accessory for singer though designed with comfort in mind (9)
I believe the answer is:
ergonomic
'accessory for singer though designed with comfort in mind' is the definition.
I can't judge whether this definition defines the answer.
'therefore expresses refusal when given' is the wordplay.
'therefore' becomes 'ergo' (I've seen this before).
'expresses refusal when' becomes 'nomic' (I am not sure about this - if you are sure you should believe this answer much more).
'given' says to put letters next to each other.
'ergo'+'nomic'='ERGONOMIC'
Can you help me to learn more?
(Other definitions for ergonomic that I've seen before include "Studying man in his work environment" , "Designed for work efficiency" , "Well-designed" , "Maximising efficiency" , "Designed for efficiency and comfort in the working environment" .)