Not easy to get river pilot at first (4)
I believe the answer is:
deep
'not easy' is the definition.
I can't judge whether this definition defines the answer.
'get river pilot at first' is the wordplay.
'get' says to put letters next to each other.
'river' becomes 'dee' (River Dee).
'at first' says to take the initial letters.
The first letter of 'pilot' is 'p'.
'dee' next to 'p' is 'DEEP'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for deep that I've seen before include "greatly involved?" , "Main" , "Mysterious" , "hard to follow" , "hard to understand" .)