The story
Blend of dime + cornerback. Modelled on quarterback: both the quarter (“25 cents”) and the dime (“10 cents”) are American coins, though quarterback was not named for the coin. Coined due to the dimeback being one additional defensive back more than the nickelback, since the 10-cent dime is more than the 5-cent nickel. See more at nickelback.
Etymology from Wiktionary, CC BY-SA 4.0.