One who follows march in dull clothes (5)
I believe the answer is:
hindu
'one who follows' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'march in dull clothes' is the wordplay.
'clothes' indicates a hidden word (the letters clothe the hidden word).
'HINDU' is hidden in the letters of 'march in dull'.
Can you help me to learn more?
(Other definitions for hindu that I've seen before include "Religious believer" , "One expecting to be reincarnated" , "Adherent to dominant religion of India" , "Adherent of an eastern religion" , "Brahma is one of his gods" .)