Old skeptic is one of six (7)
I believe the answer is:
anagram
'old skeptic' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'one of six' is the wordplay.
I cannot really understand how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for anagram that I've seen before include ""Angered" of "enraged", perhaps?" , "Word formed by changing the order of letters in another" , "pouring the tea?" , ""Supersonic"of "percussion", for example?" , "Rearrangement of letters in word or phrase to form another" .)