Dress code first introduced in capital (6)
I believe the answer is:
tunics
'dress code first introduced in capital' is the definition.
I can't tell whether this definition defines the answer.
'code first introduced in capital' is the wordplay.
'code first' becomes 'c' (1st letter of 'code').
'introduced in' indicates putting letters inside.
'capital' becomes 'Tunis' (capital of Tunisia).
'c' placed inside 'tunis' is 'TUNICS'.
Can you help me to learn more?
(Other definitions for tunics that I've seen before include "Parts of uniforms of school or military" , "'Belted jackets, parts of uniforms (6)'" , "Uniform jackets" , "Military jackets" .)