Coster's companion? (6)
I believe the answer is:
escort
'companion?' is the definition.
(escort is a kind of companion)
'coster's' is the wordplay.
'coster' anagrams to 'ESCORT'.
But, I'm unsure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for escort that I've seen before include "giving protection" , "Business providing companions for an evening out" , "Person(s) accompanying someone or something as protection" , "Protective companion" , "Companion: train" .)