Diddle involves deceit or manipulation, often linked to cheating or swindling; fiddle can mean to tinker or adjust something, but also refers to playing the violin.
The cashier gypped me when he gave me too little change Con Commit to memory; learn by heart; Have you memorized your lines for the play yet? Con On the negative side; Much was written pro and con Common Curiosities What does "con" mean in decision-making? In decision-making, "con" ...