One having thoughts of wet weather at Beachy Head (5)
I believe the answer is:
brain
'one having thoughts' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'wet weather at beachy head' is the wordplay.
'wet weather' becomes 'rain' (rain is wet weather).
'at' means one lot of letters go next to another (I've seen this in other clues).
'head' indicates taking the first letters.
The first letter of 'beachy' is 'b'.
'rain' put after 'b' is 'BRAIN'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for brain that I've seen before include "Whack on the head" , "Seat of the intellect" , "Intellectual ability" , "It controls the central nervous system" , "Mastermind" .)