Yours truly featured in publication about dark arts (5)
I believe the answer is:
magic
'dark arts' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Maybe there's an association between them I don't understand?
'yours truly featured in publication about' is the wordplay.
'yours truly' becomes 'I' (the person who set this crossword).
'featured in' means one lot of letters goes inside another.
'publication' becomes 'mag' (abbreviation for magazine).
'about' becomes 'c' (abbreviation for circa).
'mag'+'c'='magc'
'i' placed into 'magc' is 'MAGIC'.
Can you help me to learn more?
(Other definitions for magic that I've seen before include "Enchantment" , "Prestidigitation" , "Wonderful" , "'Charms, spells, illusions (5)'" , "Mysterious quality" .)