One showing the way to a raving lunatic (9)
I believe the answer is:
navigator
'one showing the way' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'to a raving lunatic' is the wordplay.
'lunatic' is an anagram indicator.
'to'+'a'+'raving'='toaraving'
'toaraving' anagrammed gives 'NAVIGATOR'.
Can you help me to learn more?
(Other definitions for navigator that I've seen before include "crew member" , "For example, Henry" , "One directs the course, of a ship say" , "Assistant to driver" , "Marine explorer" .)