Article or essay's backing conjecture (6)
I believe the answer is:
theory
'conjecture' is the definition.
(I've seen this in another clue)
'article or essay's backing' is the wordplay.
'article' becomes 'the' (the definite article).
'backing' says to take the final letters.
The last letter of 'essay' is 'y'.
'the'+'or'+'y'='THEORY'
(Other definitions for theory that I've seen before include "Idea to explain something, say evolution" , "Conjectural view" , "A conjecture to explain something" , "Hypothesis, thesis" , "Guess" .)