Priceless coat lost by child, the first of several to go missing (9)
I believe the answer is:
hilarious
'priceless' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for hilarious that I've seen before include "Priceless!" , "Extremely amusing" , "Louis' hair! (anag)" , "Extremely funny" , "Uriah's oil (anag.)" .)