Clue: Truth backed by notes of confession making one quarrelsome (8)
Answer: FACTIOUS
Explanation: Truth backed by notes of confession making one quarrelsome (8)
**FACT** ("truth") backed by** IOUs** ("notes of confession") 
*The grammar in this clue is wrong, in my opinion, as the "one" in the clue is at best superfluous, as it leads the solver to look for a noun ie "one (who is) fractious", rather than the adjectival solution.