Old one suspects the local fool (6)
I believe the answer is:
Here is my best explanation:
'the local fool' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'old one suspects' is the subsidiary indication.
'old one' anagrams to 'noodle'.
However, I am not sure how the anagram is indicated.
(Other definitions for noodle that I've seen before include "In slang, a foolish person or just the head", "bit of a dish", "Head - simpleton - found in soup", "Ribbon strip of pasta", "Thin strand of pasta", "bit of pasta", "String of pasta", "Simple person - in the soup?", "Ribbon-like strip of pasta" and "Slangy head or pasta strip".)