Entering harbour, just losing way, a trip provider (9)
I believe the answer is:
marijuana
'trip provider' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'entering harbour just losing way a' is the wordplay.
'entering' is an insertion indicator.
'harbour' becomes 'marina' (marina is a type of harbour).
'just losing way' becomes 'ju' (I can't explain this - if you can you should believe this answer much more).
'ju'+'a'='jua'
'marina' going around 'jua' is 'MARIJUANA'.
Can you help me to learn more?
(Other definitions for marijuana that I've seen before include "Wacky baccy" , "Hemp" , "Recreational drug" , "Cannabis" , "3 Down" .)