Scheme that includes one who knows all the coastal hazards (5)
I believe the answer is:
pilot
'scheme that includes one who knows all the coastal hazards' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'scheme that includes one' is the wordplay.
'scheme' becomes 'plot' (plot is a kind of scheme).
'that includes' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'plot' enclosing 'i' is 'PILOT'.
Can you help me to learn more?
(Other definitions for pilot that I've seen before include "Flier of aircraft" , "trial episode" , "Aircraft captain" , "Name of Mr Rochester's dog" , "Navigator" .)