Anxiety, when cap is removed to reveal hair (5)
I believe the answer is:
tress
'hair' is the definition.
(I know that tress is a type of coif)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for tress that I've seen before include "Rests (anag.)" , "Obsolete support" , "Long lock or plait of hair" , "Bit of hair" , "Switch" .)